Replace String::compose with fmt::format().

author: Carl Hetherington <cth@carlh.net> 2024-12-23 21:53:32 +0100
committer: Carl Hetherington <cth@carlh.net> 2024-12-26 00:27:08 +0100
commit: 8caf013a9b8d709ed7c3d5e9febee0067e6fcf1f (patch)
tree: 40da87cb357e8b1c54a1464bdbac2d014640e30c
parent: cec6ff92aef45c687085ecfc1059004407c18c57 (diff)
143 files changed, 808 insertions, 1206 deletions
diff --git a/src/lib/analytics.cc b/src/lib/analytics.cc
index b3c44202a..efb737a8e 100644
--- a/src/lib/analytics.cc
+++ b/src/lib/analytics.cc
@@ -20,7 +20,6 @@
 
 
 #include "analytics.h"
-#include "compose.hpp"
 #include "exceptions.h"
 #include "variant.h"
 #include <dcp/filesystem.h>
@@ -61,18 +60,18 @@ Analytics::successful_dcp_encode ()
 			boost::bind(
 				boost::ref(Message),
 				_("Congratulations!"),
-				String::compose(_(
-					"<h2>You have made %1 DCPs with %2!</h2>"
+				fmt::format(_(
+					"<h2>You have made {} DCPs with {}!</h2>"
 					"<img width=\"20%%\" src=\"memory:me.jpg\" align=\"center\">"
 					"<font size=\"+1\">"
                                         "<p>Hello. I'm Carl and I'm the "
-					"developer of %3. I work on it in my spare time (with the help "
+					"developer of {}. I work on it in my spare time (with the help "
 					"of a fine volunteer team of testers and translators) and I release it "
 					"as free software."
 
-					"<p>If you find %4 useful, please consider a donation to the "
+					"<p>If you find {} useful, please consider a donation to the "
 					"project. Financial support will help me to spend more "
-					"time developing %5 and making it better!"
+					"time developing {} and making it better!"
 
 					"<p><ul>"
 					"<li><a href=\"https://dcpomatic.com/donate_amount?amount=40\">Go to Paypal to donate €40</a>"
diff --git a/src/lib/atmos_mxf_content.cc b/src/lib/atmos_mxf_content.cc
index 6b2a64d68..dffebd9b0 100644
--- a/src/lib/atmos_mxf_content.cc
+++ b/src/lib/atmos_mxf_content.cc
@@ -21,12 +21,12 @@
 
 #include "atmos_content.h"
 #include "atmos_mxf_content.h"
-#include "compose.hpp"
 #include "film.h"
 #include "job.h"
 #include <asdcp/KM_log.h>
 #include <dcp/atmos_asset.h>
 #include <dcp/exceptions.h>
+#include <fmt/format.h>
 #include <libxml++/libxml++.h>
 
 #include "i18n.h"
@@ -93,7 +93,7 @@ AtmosMXFContent::examine (shared_ptr<const Film> film, shared_ptr<Job> job)
 string
 AtmosMXFContent::summary () const
 {
-	return String::compose (_("%1 [Atmos]"), path_summary());
+	return fmt::format(_("{} [Atmos]"), path_summary());
 }
 
 
diff --git a/src/lib/audio_analyser.cc b/src/lib/audio_analyser.cc
index 6e7b9fa86..7d4ee6ace 100644
--- a/src/lib/audio_analyser.cc
+++ b/src/lib/audio_analyser.cc
@@ -135,7 +135,7 @@ AudioAnalyser::AudioAnalyser(shared_ptr<const Film> film, shared_ptr<const Playl
 void
 AudioAnalyser::analyse (shared_ptr<AudioBuffers> b, DCPTime time)
 {
-	LOG_DEBUG_AUDIO_ANALYSIS("AudioAnalyser received %1 frames at %2", b->frames(), to_string(time));
+	LOG_DEBUG_AUDIO_ANALYSIS("AudioAnalyser received {} frames at {}", b->frames(), to_string(time));
 	DCPOMATIC_ASSERT (time >= _start);
 	/* In bug #2364 we had a lot of frames arriving here (~47s worth) which
 	 * caused an OOM error on Windows.  Check for the number of frames being
diff --git a/src/lib/audio_content.cc b/src/lib/audio_content.cc
index bda0230ca..20024b0ec 100644
--- a/src/lib/audio_content.cc
+++ b/src/lib/audio_content.cc
@@ -20,7 +20,6 @@
 
 
 #include "audio_content.h"
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "exceptions.h"
@@ -153,7 +152,7 @@ AudioContent::technical_summary () const
 {
 	string s = "audio: ";
 	for (auto i: streams()) {
-		s += String::compose ("stream channels %1 rate %2 ", i->channels(), i->frame_rate());
+		s += fmt::format("stream channels {} rate {} ", i->channels(), i->frame_rate());
 	}
 
 	return s;
@@ -266,14 +265,14 @@ AudioContent::processing_description (shared_ptr<const Film> film) const
 	}
 
 	if (not_resampled && resampled) {
-		return String::compose (_("Some audio will be resampled to %1Hz"), resampled_frame_rate(film));
+		return fmt::format(_("Some audio will be resampled to {}Hz"), resampled_frame_rate(film));
 	}
 
 	if (!not_resampled && resampled) {
 		if (same) {
-			return String::compose (_("Audio will be resampled from %1Hz to %2Hz"), common_frame_rate.get(), resampled_frame_rate(film));
+			return fmt::format(_("Audio will be resampled from {}Hz to {}Hz"), common_frame_rate.get(), resampled_frame_rate(film));
 		} else {
-			return String::compose (_("Audio will be resampled to %1Hz"), resampled_frame_rate(film));
+			return fmt::format(_("Audio will be resampled to {}Hz"), resampled_frame_rate(film));
 		}
 	}
 
@@ -291,7 +290,7 @@ AudioContent::channel_names () const
 	int stream = 1;
 	for (auto i: streams()) {
 		for (int j = 0; j < i->channels(); ++j) {
-			n.push_back (NamedChannel(String::compose ("%1:%2", stream, j + 1), index++));
+			n.push_back (NamedChannel(fmt::format("{}:{}", stream, j + 1), index++));
 		}
 		++stream;
 	}
diff --git a/src/lib/audio_decoder.cc b/src/lib/audio_decoder.cc
index 60b0f07ad..9dd57f32a 100644
--- a/src/lib/audio_decoder.cc
+++ b/src/lib/audio_decoder.cc
@@ -25,7 +25,6 @@
 #include "dcpomatic_log.h"
 #include "log.h"
 #include "resampler.h"
-#include "compose.hpp"
 #include <iostream>
 
 #include "i18n.h"
@@ -84,7 +83,7 @@ AudioDecoder::emit(shared_ptr<const Film> film, AudioStreamPtr stream, shared_pt
 
 	if (need_reset) {
 		LOG_GENERAL (
-			"Reset audio position: was %1, new data at %2, slack: %3 frames (more than threshold %4)",
+			"Reset audio position: was {}, new data at {}, slack: {} frames (more than threshold {})",
 			_positions[stream],
 			time.frames_round(resampled_rate),
 			std::abs(_positions[stream] - time.frames_round(resampled_rate)),
@@ -107,7 +106,7 @@ AudioDecoder::emit(shared_ptr<const Film> film, AudioStreamPtr stream, shared_pt
 	} else {
 		if (stream->frame_rate() != resampled_rate) {
 			LOG_GENERAL (
-				"Creating new resampler from %1 to %2 with %3 channels",
+				"Creating new resampler from {} to {} with {} channels",
 				stream->frame_rate(),
 				resampled_rate,
 				stream->channels()
@@ -128,7 +127,7 @@ AudioDecoder::emit(shared_ptr<const Film> film, AudioStreamPtr stream, shared_pt
 		 * here.
 		 */
 		if (resampler->channels() != data->channels()) {
-			LOG_WARNING("Received audio data with an unexpected channel count of %1 instead of %2", data->channels(), resampler->channels());
+			LOG_WARNING("Received audio data with an unexpected channel count of {} instead of {}", data->channels(), resampler->channels());
 			auto data_copy = data->clone();
 			data_copy->set_channels(resampler->channels());
 			data = resampler->run(data_copy);
diff --git a/src/lib/audio_filter_graph.cc b/src/lib/audio_filter_graph.cc
index 55a26cdb2..7f7e87888 100644
--- a/src/lib/audio_filter_graph.cc
+++ b/src/lib/audio_filter_graph.cc
@@ -21,7 +21,6 @@
 
 #include "audio_buffers.h"
 #include "audio_filter_graph.h"
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
 #include "exceptions.h"
 extern "C" {
@@ -30,6 +29,7 @@ extern "C" {
 #include <libavutil/channel_layout.h>
 #include <libavutil/opt.h>
 }
+#include <fmt/format.h>
 #include <iostream>
 
 #include "i18n.h"
@@ -154,7 +154,7 @@ AudioFilterGraph::process (shared_ptr<AudioBuffers> buffers)
 	if (r < 0) {
 		char buffer[256];
 		av_strerror (r, buffer, sizeof(buffer));
-		throw DecodeError (String::compose (N_("could not push buffer into filter chain (%1)"), &buffer[0]));
+		throw DecodeError(fmt::format(N_("could not push buffer into filter chain ({})"), &buffer[0]));
 	}
 
 	while (true) {
diff --git a/src/lib/butler.cc b/src/lib/butler.cc
index dd9874587..a684ec77c 100644
--- a/src/lib/butler.cc
+++ b/src/lib/butler.cc
@@ -20,7 +20,6 @@
 
 
 #include "butler.h"
-#include "compose.hpp"
 #include "cross.h"
 #include "dcpomatic_log.h"
 #include "exceptions.h"
@@ -105,7 +104,7 @@ Butler::Butler (
 	   multi-thread JPEG2000 decoding.
 	*/
 
-	LOG_TIMING("start-prepare-threads %1", boost::thread::hardware_concurrency() * 2);
+	LOG_TIMING("start-prepare-threads {}", boost::thread::hardware_concurrency() * 2);
 
 	for (size_t i = 0; i < boost::thread::hardware_concurrency() * 2; ++i) {
 		_prepare_pool.create_thread (bind (&boost::asio::io_service::run, &_prepare_service));
@@ -141,10 +140,10 @@ Butler::should_run () const
 		auto pos = _audio.peek();
 		if (pos) {
 			throw ProgrammingError
-				(__FILE__, __LINE__, String::compose ("Butler video buffers reached %1 frames (audio is %2 at %3)", _video.size(), _audio.size(), pos->get()));
+				(__FILE__, __LINE__, fmt::format("Butler video buffers reached {} frames (audio is {} at {})", _video.size(), _audio.size(), pos->get()));
 		} else {
 			throw ProgrammingError
-				(__FILE__, __LINE__, String::compose ("Butler video buffers reached %1 frames (audio is %2)", _video.size(), _audio.size()));
+				(__FILE__, __LINE__, fmt::format("Butler video buffers reached {} frames (audio is {})", _video.size(), _audio.size()));
 		}
 	}
 
@@ -153,19 +152,19 @@ Butler::should_run () const
 		auto pos = _audio.peek();
 		if (pos) {
 			throw ProgrammingError
-				(__FILE__, __LINE__, String::compose ("Butler audio buffers reached %1 frames at %2 (video is %3)", _audio.size(), pos->get(), _video.size()));
+				(__FILE__, __LINE__, fmt::format("Butler audio buffers reached {} frames at {} (video is {})", _audio.size(), pos->get(), _video.size()));
 		} else {
 			throw ProgrammingError
-				(__FILE__, __LINE__, String::compose ("Butler audio buffers reached %1 frames (video is %3)", _audio.size(), _video.size()));
+				(__FILE__, __LINE__, fmt::format("Butler audio buffers reached {} frames (video is {})", _audio.size(), _video.size()));
 		}
 	}
 
 	if (_video.size() >= MAXIMUM_VIDEO_READAHEAD * 2) {
-		LOG_WARNING ("Butler video buffers reached %1 frames (audio is %2)", _video.size(), _audio.size());
+		LOG_WARNING("Butler video buffers reached {} frames (audio is {})", _video.size(), _audio.size());
 	}
 
 	if (_audio.size() >= MAXIMUM_AUDIO_READAHEAD * 2) {
-		LOG_WARNING ("Butler audio buffers reached %1 frames (video is %2)", _audio.size(), _video.size());
+		LOG_WARNING("Butler audio buffers reached {} frames (video is {})", _audio.size(), _video.size());
 	}
 
 	if (_stop_thread || _finished || _died || _suspended) {
@@ -325,9 +324,9 @@ try
 	auto video = weak_video.lock ();
 	/* If the weak_ptr cannot be locked the video obviously no longer requires any work */
 	if (video) {
-		LOG_TIMING("start-prepare in %1", thread_id());
+		LOG_TIMING("start-prepare in {}", thread_id());
 		video->prepare (_pixel_format, _video_range, _alignment, _fast, _prepare_only_proxy);
-		LOG_TIMING("finish-prepare in %1", thread_id());
+		LOG_TIMING("finish-prepare in {}", thread_id());
 	}
 }
 catch (std::exception& e)
@@ -473,7 +472,7 @@ Butler::Error::summary () const
 		case Error::Code::AGAIN:
 			return "Butler not ready";
 		case Error::Code::DIED:
-			return String::compose("Butler died (%1)", message);
+			return fmt::format("Butler died ({})", message);
 		case Error::Code::FINISHED:
 			return "Butler finished";
 	}
diff --git a/src/lib/cinema_list.cc b/src/lib/cinema_list.cc
index 41b9dbab3..e6ec6b34f 100644
--- a/src/lib/cinema_list.cc
+++ b/src/lib/cinema_list.cc
@@ -30,6 +30,7 @@
 #include "util.h"
 #include <dcp/certificate.h>
 #include <sqlite3.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <iostream>
 #include <numeric>
@@ -153,7 +154,7 @@ void
 CinemaList::clear()
 {
 	for (auto table: { "cinemas", "screens", "trusted_devices" }) {
-		SQLiteStatement sql(_db, String::compose("DELETE FROM %1", table));
+		SQLiteStatement sql(_db, fmt::format("DELETE FROM {}", table));
 		sql.execute();
 	}
 }
diff --git a/src/lib/collator.cc b/src/lib/collator.cc
index 8de1857ab..08d5bb2ae 100644
--- a/src/lib/collator.cc
+++ b/src/lib/collator.cc
@@ -27,6 +27,7 @@
 #include <unicode/utypes.h>
 #include <unicode/usearch.h>
 #include <unicode/ustring.h>
+#include <boost/algorithm/string.hpp>
 #include <boost/scoped_array.hpp>
 #include <cstring>
 #include <vector>
diff --git a/src/lib/combine_dcp_job.cc b/src/lib/combine_dcp_job.cc
index 5c299492b..5afcb04b4 100644
--- a/src/lib/combine_dcp_job.cc
+++ b/src/lib/combine_dcp_job.cc
@@ -20,10 +20,10 @@
 
 
 #include "combine_dcp_job.h"
-#include "compose.hpp"
 #include "config.h"
 #include <dcp/combine.h>
 #include <dcp/exceptions.h>
+#include <fmt/format.h>
 
 #include "i18n.h"
 
@@ -64,8 +64,8 @@ CombineDCPJob::run ()
 		dcp::combine (
 			_inputs,
 			_output,
-			String::compose("libdcp %1", dcp::version),
-			String::compose("libdcp %1", dcp::version),
+			fmt::format("libdcp {}", dcp::version),
+			fmt::format("libdcp {}", dcp::version),
 			dcp::LocalTime().as_string(),
 			_annotation_text,
 			Config::instance()->signer_chain()
diff --git a/src/lib/compose.hpp b/src/lib/compose.hpp
deleted file mode 100644
index 479493f14..000000000
--- a/src/lib/compose.hpp
+++ /dev/null
@@ -1,392 +0,0 @@
-/* -*- c-basic-offset: 2 -*-
- * Defines String::compose(fmt, arg...) for easy, i18n-friendly
- * composition of strings.
- *
- * Version 1.0.
- *
- * Copyright (c) 2002 Ole Laursen <olau@hardworking.dk>.
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public License
- * as published by the Free Software Foundation; either version 2.1 of
- * the License, or (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
- * Lesser General Public License for more details.
- *
- * You should have received a copy of the GNU Lesser General Public
- * License along with this library; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
- * USA.
- */
-
-//
-// Basic usage is like
-//
-//   std::cout << String::compose("This is a %1x%2 matrix.", rows, cols);
-//
-// See http://www.cs.aau.dk/~olau/compose/ or the included README.compose for
-// more details.
-//
-
-#ifndef DCPOMATIC_STRING_COMPOSE_H
-#define DCPOMATIC_STRING_COMPOSE_H
-
-#include <dcp/locale_convert.h>
-#include <boost/filesystem.hpp>
-#include <string>
-#include <list>
-#include <map>
-#include <inttypes.h>
-#include <cstdio>
-
-namespace StringPrivate
-{
-  // the actual composition class - using string::compose is cleaner, so we
-  // hide it here
-  class Composition
-  {
-  public:
-    // initialize and prepare format string on the form "text %1 text %2 etc."
-    explicit Composition(std::string fmt);
-
-    // supply an replacement argument starting from %1
-    template <typename T>
-    Composition &arg(const T &obj);
-
-    // compose and return string
-    std::string str() const;
-
-  private:
-    std::string os;
-    int arg_no;
-
-    // we store the output as a list - when the output string is requested, the
-    // list is concatenated to a string; this way we can keep iterators into
-    // the list instead of into a string where they're possibly invalidated on
-    // inserting a specification string
-    typedef std::list<std::string> output_list;
-    output_list output;
-
-    // the initial parse of the format string fills in the specification map
-    // with positions for each of the various %?s
-    typedef std::multimap<int, output_list::iterator> specification_map;
-    specification_map specs;
-  };
-
-  // helper for converting spec string numbers
-  inline int char_to_int(char c)
-  {
-    switch (c) {
-    case '0': return 0;
-    case '1': return 1;
-    case '2': return 2;
-    case '3': return 3;
-    case '4': return 4;
-    case '5': return 5;
-    case '6': return 6;
-    case '7': return 7;
-    case '8': return 8;
-    case '9': return 9;
-    default: return -1000;
-    }
-  }
-
-  inline bool is_number(int n)
-  {
-    switch (n) {
-    case '0':
-    case '1':
-    case '2':
-    case '3':
-    case '4':
-    case '5':
-    case '6':
-    case '7':
-    case '8':
-    case '9':
-      return true;
-
-    default:
-      return false;
-    }
-  }
-
-  // implementation of class Composition
-  template <typename T>
-  inline Composition &Composition::arg(const T &obj)
-  {
-    os += dcp::locale_convert<std::string>(obj);
-
-    if (!os.empty()) {		// manipulators don't produce output
-      for (specification_map::const_iterator i = specs.lower_bound(arg_no), end = specs.upper_bound(arg_no); i != end; ++i) {
-	output_list::iterator pos = i->second;
-	++pos;
-
-	output.insert(pos, os);
-      }
-
-      os = "";
-      ++arg_no;
-    }
-
-    return *this;
-  }
-
-  inline Composition::Composition(std::string fmt)
-    : arg_no(1)
-  {
-    std::string::size_type b = 0, i = 0;
-
-    // fill in output with the strings between the %1 %2 %3 etc. and
-    // fill in specs with the positions
-    while (i < fmt.length()) {
-      if (fmt[i] == '%' && i + 1 < fmt.length()) {
-	if (fmt[i + 1] == '%') {	// catch %%
-	  fmt.replace(i, 2, "%");
-	  ++i;
-	}
-	else if (is_number(fmt[i + 1])) { // aha! a spec!
-	  // save string
-	  output.push_back(fmt.substr(b, i - b));
-
-	  int n = 1;		// number of digits
-	  int spec_no = 0;
-
-	  do {
-	    spec_no += char_to_int(fmt[i + n]);
-	    spec_no *= 10;
-	    ++n;
-	  } while (i + n < fmt.length() && is_number(fmt[i + n]));
-
-	  spec_no /= 10;
-	  output_list::iterator pos = output.end();
-	  --pos;		// safe since we have just inserted a string>
-
-	  specs.insert(specification_map::value_type(spec_no, pos));
-
-	  // jump over spec string
-	  i += n;
-	  b = i;
-	}
-	else
-	  ++i;
-      }
-      else
-	++i;
-    }
-
-    if (i - b > 0)		// add the rest of the string
-      output.push_back(fmt.substr(b, i - b));
-  }
-
-  inline std::string Composition::str() const
-  {
-    // assemble string
-    std::string str;
-
-    for (output_list::const_iterator i = output.begin(), end = output.end();
-	 i != end; ++i)
-      str += *i;
-
-    return str;
-  }
-}
-
-// now for the real thing(s)
-namespace String
-{
-  // a series of functions which accept a format string on the form "text %1
-  // more %2 less %3" and a number of templated parameters and spits out the
-  // composited string
-  template <typename T1>
-  inline std::string compose(const std::string &fmt, const T1 &o1)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1);
-    return c.str();
-  }
-
-  template <typename T1, typename T2>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7, typename T8>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7, const T8 &o8)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7).arg(o8);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7, typename T8, typename T9>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7, const T8 &o8, const T9 &o9)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7).arg(o8).arg(o9);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7, typename T8, typename T9, typename T10>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7, const T8 &o8, const T9 &o9,
-			     const T10 &o10)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7).arg(o8).arg(o9)
-      .arg(o10);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7, typename T8, typename T9, typename T10,
-	    typename T11>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7, const T8 &o8, const T9 &o9,
-			     const T10 &o10, const T11 &o11)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7).arg(o8).arg(o9)
-      .arg(o10).arg(o11);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7, typename T8, typename T9, typename T10,
-	    typename T11, typename T12>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7, const T8 &o8, const T9 &o9,
-			     const T10 &o10, const T11 &o11, const T12 &o12)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7).arg(o8).arg(o9)
-      .arg(o10).arg(o11).arg(o12);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7, typename T8, typename T9, typename T10,
-	    typename T11, typename T12, typename T13>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7, const T8 &o8, const T9 &o9,
-			     const T10 &o10, const T11 &o11, const T12 &o12,
-			     const T13 &o13)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7).arg(o8).arg(o9)
-      .arg(o10).arg(o11).arg(o12).arg(o13);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7, typename T8, typename T9, typename T10,
-	    typename T11, typename T12, typename T13, typename T14>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7, const T8 &o8, const T9 &o9,
-			     const T10 &o10, const T11 &o11, const T12 &o12,
-			     const T13 &o13, const T14 &o14)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7).arg(o8).arg(o9)
-      .arg(o10).arg(o11).arg(o12).arg(o13).arg(o14);
-    return c.str();
-  }
-
-  template <typename T1, typename T2, typename T3, typename T4, typename T5,
-	    typename T6, typename T7, typename T8, typename T9, typename T10,
-	    typename T11, typename T12, typename T13, typename T14,
-	    typename T15>
-  inline std::string compose(const std::string &fmt,
-			     const T1 &o1, const T2 &o2, const T3 &o3,
-			     const T4 &o4, const T5 &o5, const T6 &o6,
-			     const T7 &o7, const T8 &o8, const T9 &o9,
-			     const T10 &o10, const T11 &o11, const T12 &o12,
-			     const T13 &o13, const T14 &o14, const T15 &o15)
-  {
-    StringPrivate::Composition c(fmt);
-    c.arg(o1).arg(o2).arg(o3).arg(o4).arg(o5).arg(o6).arg(o7).arg(o8).arg(o9)
-      .arg(o10).arg(o11).arg(o12).arg(o13).arg(o14).arg(o15);
-    return c.str();
-  }
-}
-
-
-#endif // STRING_COMPOSE_H
diff --git a/src/lib/config.cc b/src/lib/config.cc
index 1c6e50a28..e4b01b872 100644
--- a/src/lib/config.cc
+++ b/src/lib/config.cc
@@ -21,7 +21,6 @@
 
 #include "cinema_list.h"
 #include "colour_conversion.h"
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "cross.h"
@@ -41,6 +40,7 @@
 #include <libcxml/cxml.h>
 #include <glib.h>
 #include <libxml++/libxml++.h>
+#include <fmt/format.h>
 #include <boost/filesystem.hpp>
 #include <boost/algorithm/string.hpp>
 #include <boost/thread.hpp>
@@ -273,7 +273,7 @@ Config::backup ()
 	auto copy_adding_number = [](path const& path_to_copy) {
 
 		auto add_number = [](path const& path, int number) {
-			return String::compose("%1.%2", path, number);
+			return fmt::format("{}.{}", path.string(), number);
 		};
 
 		int n = 1;
@@ -435,7 +435,7 @@ try
 	_kdm_bcc = f.optional_string_child ("KDMBCC").get_value_or ("");
 	_kdm_email = f.string_child ("KDMEmail");
 
-	_notification_subject = f.optional_string_child("NotificationSubject").get_value_or(variant::insert_dcpomatic(_("%1 notification")));
+	_notification_subject = f.optional_string_child("NotificationSubject").get_value_or(variant::insert_dcpomatic(_("{} notification")));
 	_notification_from = f.optional_string_child("NotificationFrom").get_value_or("");
 	_notification_to = f.optional_string_child("NotificationTo").get_value_or("");
 	for (auto i: f.node_children("NotificationCC")) {
@@ -1244,14 +1244,14 @@ Config::set_kdm_email_to_default ()
 		"Cinema: $CINEMA_NAME\n"
 		"Screen(s): $SCREENS\n\n"
 		"The KDMs are valid from $START_TIME until $END_TIME.\n\n"
-		"Best regards,\n%1"
+		"Best regards,\n{}"
 		));
 }
 
 void
 Config::set_notification_email_to_default ()
 {
-	_notification_subject = variant::insert_dcpomatic(_("%1 notification"));
+	_notification_subject = variant::insert_dcpomatic(_("{} notification"));
 
 	_notification_email = _(
 		"$JOB_NAME: $JOB_STATUS"
diff --git a/src/lib/content.cc b/src/lib/content.cc
index 5c44cb47a..0abb061c8 100644
--- a/src/lib/content.cc
+++ b/src/lib/content.cc
@@ -26,7 +26,6 @@
 
 #include "audio_content.h"
 #include "change_signaller.h"
-#include "compose.hpp"
 #include "content.h"
 #include "content_factory.h"
 #include "exceptions.h"
@@ -309,9 +308,9 @@ Content::clone() const
 string
 Content::technical_summary () const
 {
-	auto s = String::compose ("%1 %2 %3", path_summary(), digest(), position().seconds());
+	auto s = fmt::format("{} {} {}", path_summary(), digest(), position().seconds());
 	if (_video_frame_rate) {
-		s += String::compose(" %1", *_video_frame_rate);
+		s += fmt::format(" {}", *_video_frame_rate);
 	}
 	return s;
 }
@@ -478,7 +477,7 @@ Content::add_properties (shared_ptr<const Film>, list<UserProperty>& p) const
 		}
 	}
 	if (paths_to_show < number_of_paths()) {
-		paths += String::compose("... and %1 more", number_of_paths() - paths_to_show);
+		paths += fmt::format("... and {} more", number_of_paths() - paths_to_show);
 	}
 	p.push_back (
 		UserProperty(
diff --git a/src/lib/content_factory.cc b/src/lib/content_factory.cc
index 5d36c2aea..012aa2fb4 100644
--- a/src/lib/content_factory.cc
+++ b/src/lib/content_factory.cc
@@ -38,7 +38,6 @@
 #include "log_entry.h"
 #include "dcpomatic_log.h"
 #include "log.h"
-#include "compose.hpp"
 #include <libcxml/cxml.h>
 #include <dcp/filesystem.h>
 #include <dcp/smpte_text_asset.h>
@@ -114,7 +113,7 @@ content_factory (boost::filesystem::path path)
 
 	if (dcp::filesystem::is_directory(path)) {
 
-		LOG_GENERAL ("Look in directory %1", path);
+		LOG_GENERAL("Look in directory {}", path.string());
 
 		if (dcp::filesystem::is_empty(path)) {
 			return content;
@@ -127,17 +126,17 @@ content_factory (boost::filesystem::path path)
 		int read = 0;
 		for (dcp::filesystem::directory_iterator i(path); i != dcp::filesystem::directory_iterator() && read < 10; ++i) {
 
-			LOG_GENERAL ("Checking file %1", i->path());
+			LOG_GENERAL("Checking file {}", i->path().string());
 
 			if (boost::starts_with(i->path().filename().string(), ".")) {
 				/* We ignore hidden files */
-				LOG_GENERAL ("Ignored %1 (starts with .)", i->path());
+				LOG_GENERAL("Ignored {} (starts with .)", i->path().string());
 				continue;
 			}
 
 			if (!dcp::filesystem::is_regular_file(i->path())) {
 				/* Ignore things which aren't files (probably directories) */
-				LOG_GENERAL ("Ignored %1 (not a regular file)", i->path());
+				LOG_GENERAL("Ignored {} (not a regular file)", i->path().string());
 				continue;
 			}
 
diff --git a/src/lib/copy_to_drive_job.cc b/src/lib/copy_to_drive_job.cc
index 4ed9421d6..b04c273ee 100644
--- a/src/lib/copy_to_drive_job.cc
+++ b/src/lib/copy_to_drive_job.cc
@@ -19,12 +19,12 @@
 */
 
 
-#include "compose.hpp"
 #include "copy_to_drive_job.h"
 #include "dcpomatic_log.h"
 #include "disk_writer_messages.h"
 #include "exceptions.h"
 #include <nanomsg/nn.h>
+#include <fmt/format.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <iostream>
@@ -56,10 +56,10 @@ string
 CopyToDriveJob::name () const
 {
 	if (_dcps.size() == 1) {
-		return String::compose(_("Copying %1\nto %2"), _dcps[0].filename().string(), _drive.description());
+		return fmt::format(_("Copying {}\nto {}"), _dcps[0].filename().string(), _drive.description());
 	}
 
-	return String::compose(_("Copying DCPs to %1"), _drive.description());
+	return fmt::format(_("Copying DCPs to {}"), _drive.description());
 }
 
 
@@ -72,14 +72,14 @@ CopyToDriveJob::json_name () const
 void
 CopyToDriveJob::run ()
 {
-	LOG_DISK("Sending write requests to disk %1 for:", _drive.device());
+	LOG_DISK("Sending write requests to disk {} for:", _drive.device());
 	for (auto dcp: _dcps) {
-		LOG_DISK("%1", dcp.string());
+		LOG_DISK("{}", dcp.string());
 	}
 
-	string request = String::compose(DISK_WRITER_WRITE "\n%1\n", _drive.device());
+	string request = fmt::format(DISK_WRITER_WRITE "\n{}\n", _drive.device());
 	for (auto dcp: _dcps) {
-		request += String::compose("%1\n", dcp.string());
+		request += fmt::format("{}\n", dcp.string());
 	}
 	request += "\n";
 	if (!_nanomsg.send(request, 2000)) {
diff --git a/src/lib/cpu_j2k_encoder_thread.cc b/src/lib/cpu_j2k_encoder_thread.cc
index 580facae9..6ff38e5da 100644
--- a/src/lib/cpu_j2k_encoder_thread.cc
+++ b/src/lib/cpu_j2k_encoder_thread.cc
@@ -44,7 +44,7 @@ void
 CPUJ2KEncoderThread::log_thread_start() const
 {
 	start_of_thread("CPUJ2KEncoder");
-	LOG_TIMING("start-encoder-thread thread=%1 server=localhost", thread_id());
+	LOG_TIMING("start-encoder-thread thread={} server=localhost", thread_id());
 }
 
 
@@ -54,7 +54,7 @@ CPUJ2KEncoderThread::encode(DCPVideo const& frame)
 	try {
 		return make_shared<dcp::ArrayData>(frame.encode_locally());
 	} catch (std::exception& e) {
-		LOG_ERROR(N_("Local encode failed (%1)"), e.what());
+		LOG_ERROR(N_("Local encode failed ({})"), e.what());
 	}
 
 	return {};
diff --git a/src/lib/create_cli.cc b/src/lib/create_cli.cc
index 3fb978f7c..a007fe078 100644
--- a/src/lib/create_cli.cc
+++ b/src/lib/create_cli.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "create_cli.h"
 #include "dcp_content_type.h"
@@ -28,6 +27,7 @@
 #include "ratio.h"
 #include "variant.h"
 #include <dcp/raw_convert.h>
+#include <fmt/format.h>
 #include <iostream>
 #include <string>
 
@@ -41,8 +41,8 @@ using boost::optional;
 
 
 string CreateCLI::_help =
-	string("\nSyntax: %1 [OPTION] <CONTENT> [OPTION] [<CONTENT> ...]\n") +
-	variant::insert_dcpomatic("  -v, --version                 show %1 version\n") +
+	string("\nSyntax: {} [OPTION] <CONTENT> [OPTION] [<CONTENT> ...]\n") +
+	variant::insert_dcpomatic("  -v, --version                 show {} version\n") +
 	"  -h, --help                    show this help\n"
 	"  -n, --name <name>             film name\n"
 	"  -t, --template <name>         template name\n"
@@ -79,7 +79,7 @@ argument_option (int& n, int argc, char* argv[], string short_name, string long_
 	}
 
 	if ((n + 1) >= argc) {
-		**error = String::compose("%1: option %2 requires an argument", argv[0], long_name);
+		**error = fmt::format("{}: option {} requires an argument", argv[0], long_name);
 		return;
 	}
 
@@ -108,14 +108,14 @@ argument_option (
 	}
 
 	if ((n + 1) >= argc) {
-		**error = String::compose("%1: option %2 requires an argument", argv[0], long_name);
+		**error = fmt::format("{}: option {} requires an argument", argv[0], long_name);
 		return;
 	}
 
 	auto const arg = argv[++n];
 	auto const value = convert(arg);
 	if (!value) {
-		*error = String::compose("%1: %2 is not valid for %3", argv[0], arg, long_name);
+		*error = fmt::format("{}: {} is not valid for {}", argv[0], arg, long_name);
 		*claimed = true;
 		return;
 	}
@@ -151,7 +151,7 @@ CreateCLI::CreateCLI (int argc, char* argv[])
 		} else if (a == "-h" || a == "--help") {
 			error = "Create a film directory (ready for making a DCP) or metadata file from some content files.\n"
 				"A film directory will be created if -o or --output is specified, otherwise a metadata file\n"
-				"will be written to stdout.\n" + String::compose(_help, argv[0]);
+				"will be written to stdout.\n" + fmt::format(_help, argv[0]);
 			return;
 		}
 
@@ -246,7 +246,7 @@ CreateCLI::CreateCLI (int argc, char* argv[])
 
 		if (!claimed) {
 			if (a.length() > 2 && a.substr(0, 2) == "--") {
-				error = String::compose("%1: unrecognised option '%2'", argv[0], a) + String::compose(_help, argv[0]);
+				error = fmt::format("{}: unrecognised option '{}'", argv[0], a) + fmt::format(_help, argv[0]);
 				return;
 			} else {
 				Content c;
@@ -281,7 +281,7 @@ CreateCLI::CreateCLI (int argc, char* argv[])
 	if (dcp_content_type_string) {
 		_dcp_content_type = DCPContentType::from_isdcf_name(*dcp_content_type_string);
 		if (!_dcp_content_type) {
-			error = String::compose("%1: unrecognised DCP content type '%2'", argv[0], *dcp_content_type_string);
+			error = fmt::format("{}: unrecognised DCP content type '{}'", argv[0], *dcp_content_type_string);
 			return;
 		}
 	}
@@ -289,7 +289,7 @@ CreateCLI::CreateCLI (int argc, char* argv[])
 	if (!container_ratio_string.empty()) {
 		_container_ratio = Ratio::from_id (container_ratio_string);
 		if (!_container_ratio) {
-			error = String::compose("%1: unrecognised container ratio %2", argv[0], container_ratio_string);
+			error = fmt::format("{}: unrecognised container ratio {}", argv[0], container_ratio_string);
 			return;
 		}
 	}
@@ -300,21 +300,21 @@ CreateCLI::CreateCLI (int argc, char* argv[])
 		} else if (*standard_string == "SMPTE") {
 			_standard = dcp::Standard::SMPTE;
 		} else {
-			error = String::compose("%1: standard must be SMPTE or interop", argv[0]);
+			error = fmt::format("{}: standard must be SMPTE or interop", argv[0]);
 			return;
 		}
 	}
 
 	if (_twod && _threed) {
-		error = String::compose("%1: specify one of --twod or --threed, not both", argv[0]);
+		error = fmt::format("{}: specify one of --twod or --threed, not both", argv[0]);
 	}
 
 	if (_no_encrypt && _encrypt) {
-		error = String::compose("%1: specify one of --no-encrypt or --encrypt, not both", argv[0]);
+		error = fmt::format("{}: specify one of --no-encrypt or --encrypt, not both", argv[0]);
 	}
 
 	if (content.empty()) {
-		error = String::compose("%1: no content specified", argv[0]);
+		error = fmt::format("{}: no content specified", argv[0]);
 		return;
 	}
 
@@ -323,7 +323,7 @@ CreateCLI::CreateCLI (int argc, char* argv[])
 	}
 
 	if (_video_bit_rate && (*_video_bit_rate < 10000000 || *_video_bit_rate > Config::instance()->maximum_video_bit_rate(VideoEncoding::JPEG2000))) {
-		error = String::compose("%1: video-bit-rate must be between 10 and %2 Mbit/s", argv[0], (Config::instance()->maximum_video_bit_rate(VideoEncoding::JPEG2000) / 1000000));
+		error = fmt::format("{}: video-bit-rate must be between 10 and {} Mbit/s", argv[0], (Config::instance()->maximum_video_bit_rate(VideoEncoding::JPEG2000) / 1000000));
 		return;
 	}
 }
diff --git a/src/lib/cross_common.cc b/src/lib/cross_common.cc
index 2e6f5c414..1aabef75e 100644
--- a/src/lib/cross_common.cc
+++ b/src/lib/cross_common.cc
@@ -20,7 +20,6 @@
 
 
 #include "cross.h"
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
 #include "dcpomatic_log.h"
 #include <dcp/warnings.h>
@@ -96,7 +95,7 @@ Drive::description () const
 		name = _("Unknown");
 	}
 
-	return String::compose(_("%1 (%2 GB) [%3]"), name, gb, _device);
+	return fmt::format(_("{} ({} GB) [{}]"), name, gb, _device);
 }
 
 
@@ -113,8 +112,8 @@ Drive::log_summary () const
 		mp = mp.substr (0, mp.length() - 1);
 	}
 
-	return String::compose(
-		"Device %1 mounted on %2 size %3 vendor %4 model %5",
+	return fmt::format(
+		"Device {} mounted on {} size {} vendor {} model {}",
 		_device, mp, _size, _vendor.get_value_or("[none]"), _model.get_value_or("[none]")
 			);
 }
diff --git a/src/lib/cross_linux.cc b/src/lib/cross_linux.cc
index be3233b32..b27d1a636 100644
--- a/src/lib/cross_linux.cc
+++ b/src/lib/cross_linux.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "cross.h"
 #include "dcpomatic_log.h"
@@ -30,6 +29,7 @@
 #include <dcp/raw_convert.h>
 #include <dcp/warnings.h>
 #include <glib.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #if BOOST_VERSION >= 106100
 #include <boost/dll/runtime_symbol_info.hpp>
@@ -108,11 +108,11 @@ void
 run_ffprobe(boost::filesystem::path content, boost::filesystem::path out, bool err, string args)
 {
 	string const redirect = err ? "2>" : ">";
-	auto const ffprobe = String::compose("ffprobe %1 \"%2\" %3 \"%4\"", args.empty() ? " " : args, content.string(), redirect, out.string());
-	LOG_GENERAL (N_("Probing with %1"), ffprobe);
+	auto const ffprobe = fmt::format("ffprobe {} \"{}\" {} \"{}\"", args.empty() ? " " : args, content.string(), redirect, out.string());
+	LOG_GENERAL (N_("Probing with {}"), ffprobe);
 	int const r = system (ffprobe.c_str());
 	if (r == -1 || (WIFEXITED(r) && WEXITSTATUS(r) != 0)) {
-		LOG_GENERAL (N_("Could not run ffprobe (system returned %1"), r);
+		LOG_GENERAL (N_("Could not run ffprobe (system returned {}"), r);
 	}
 }
 
@@ -237,7 +237,7 @@ get_mounts (string prefix)
 		if (bits.size() > 1 && boost::algorithm::starts_with(bits[0], prefix)) {
 			boost::algorithm::replace_all (bits[1], "\\040", " ");
 			mounts.push_back(make_pair(bits[0], bits[1]));
-			LOG_DISK("Found mounted device %1 from prefix %2", bits[0], prefix);
+			LOG_DISK("Found mounted device {} from prefix {}", bits[0], prefix);
 		}
 	}
 
@@ -297,7 +297,7 @@ Drive::unmount ()
 {
 	for (auto i: _mount_points) {
 		int const r = umount(i.string().c_str());
-		LOG_DISK("Tried to unmount %1 and got %2 and %3", i.string(), r, errno);
+		LOG_DISK("Tried to unmount {} and got {} and {}", i.string(), r, errno);
 		if (r == -1) {
 			return false;
 		}
@@ -330,12 +330,12 @@ show_in_file_manager (boost::filesystem::path dir, boost::filesystem::path)
 {
 	int r = system ("which nautilus");
 	if (WEXITSTATUS(r) == 0) {
-		r = system (String::compose("nautilus \"%1\"", dir.string()).c_str());
+		r = system(fmt::format("nautilus \"{}\"", dir.string()).c_str());
 		return static_cast<bool>(WEXITSTATUS(r));
 	} else {
 		int r = system ("which konqueror");
 		if (WEXITSTATUS(r) == 0) {
-			r = system (String::compose("konqueror \"%1\"", dir.string()).c_str());
+			r = system(fmt::format("konqueror \"{}\"", dir.string()).c_str());
 			return static_cast<bool>(WEXITSTATUS(r));
 		}
 	}
diff --git a/src/lib/cross_osx.cc b/src/lib/cross_osx.cc
index a201cc5f9..3d2407c89 100644
--- a/src/lib/cross_osx.cc
+++ b/src/lib/cross_osx.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "cross.h"
 #include "dcpomatic_log.h"
@@ -28,6 +27,7 @@
 #include "variant.h"
 #include <dcp/filesystem.h>
 #include <glib.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <boost/regex.hpp>
 #if BOOST_VERSION >= 106100
@@ -113,8 +113,8 @@ run_ffprobe(boost::filesystem::path content, boost::filesystem::path out, bool e
 	}
 	string const redirect = err ? "2>" : ">";
 
-	auto const ffprobe = String::compose("\"%1\" %2 \"%3\" %4 \"%5\"", path, args.empty() ? " " : args, content.string(), redirect, out.string());
-	LOG_GENERAL (N_("Probing with %1"), ffprobe);
+	auto const ffprobe = fmt::format("\"{}\" {} \"{}\" {} \"{}\"", path, args.empty() ? " " : args, content.string(), redirect, out.string());
+	LOG_GENERAL(N_("Probing with {}"), ffprobe);
 	system (ffprobe.c_str());
 }
 
@@ -181,7 +181,7 @@ start_tool (string executable, string app)
 
 	pid_t pid = fork ();
 	if (pid == 0) {
-		LOG_GENERAL ("start_tool %1 %2 with path %3", executable, app, exe_path.string());
+		LOG_GENERAL("start_tool {} {} with path {}", executable, app, exe_path.string());
 		int const r = system (exe_path.string().c_str());
 		exit (WEXITSTATUS (r));
 	} else if (pid == -1) {
@@ -278,18 +278,18 @@ disk_appeared (DADiskRef disk, void* context)
 		LOG_DISK_NC("Disk with no BSDName appeared");
 		return;
 	}
-	LOG_DISK("%1 appeared", bsd_name);
+	LOG_DISK("{} appeared", bsd_name);
 
 	OSXDisk this_disk;
 
 	this_disk.device = string("/dev/") + bsd_name;
-	LOG_DISK("Device is %1", this_disk.device);
+	LOG_DISK("Device is {}", this_disk.device);
 
 	CFDictionaryRef description = DADiskCopyDescription (disk);
 
 	this_disk.vendor = get_vendor (description);
 	this_disk.model = get_model (description);
-	LOG_DISK("Vendor/model: %1 %2", this_disk.vendor.get_value_or("[none]"), this_disk.model.get_value_or("[none]"));
+	LOG_DISK("Vendor/model: {} {}", this_disk.vendor.get_value_or("[none]"), this_disk.model.get_value_or("[none]"));
 
 	auto mp = mount_point (description);
 	if (mp) {
@@ -307,7 +307,7 @@ disk_appeared (DADiskRef disk, void* context)
 	this_disk.partition = string(bsd_name).find("s", 5) != std::string::npos;
 
 	LOG_DISK(
-		"%1 %2 %3 %4 mounted at %5",
+		"{} {} {} {} mounted at {}",
 		bsd_name,
 		this_disk.system ? "system" : "non-system",
 		this_disk.writeable ? "writeable" : "read-only",
@@ -352,9 +352,9 @@ Drive::get ()
 		}
 	}
 
-	LOG_DISK("Drive::get() found %1 drives:", drives.size());
+	LOG_DISK("Drive::get() found {} drives:", drives.size());
 	for (auto const& drive: drives) {
-		LOG_DISK("%1 %2 mounted=%3", drive.description(), drive.device(), drive.mounted() ? "yes" : "no");
+		LOG_DISK("{} {} mounted={}", drive.description(), drive.device(), drive.mounted() ? "yes" : "no");
 	}
 
 	return drives;
@@ -390,7 +390,7 @@ void done_callback(DADiskRef, DADissenterRef dissenter, void* context)
 	auto state = reinterpret_cast<UnmountState*>(context);
 	state->callback = true;
 	if (dissenter) {
-		LOG_DISK("Error: %1", DADissenterGetStatus(dissenter));
+		LOG_DISK("Error: {}", DADissenterGetStatus(dissenter));
 	} else {
 		LOG_DISK_NC("Successful");
 		state->success = true;
@@ -412,7 +412,7 @@ Drive::unmount ()
 	if (!disk) {
 		return false;
 	}
-	LOG_DISK("Requesting unmount of %1 from %2", _device, thread_id());
+	LOG_DISK("Requesting unmount of {} from {}", _device, thread_id());
 	UnmountState state;
 	DADiskUnmount(disk, kDADiskUnmountOptionWhole, &done_callback, &state);
 	CFRelease (disk);
@@ -426,7 +426,7 @@ Drive::unmount ()
 	if (!state.callback) {
 		LOG_DISK_NC("End of unmount: timeout");
 	} else {
-		LOG_DISK("End of unmount: %1", state.success ? "success" : "failure");
+		LOG_DISK("End of unmount: {}", state.success ? "success" : "failure");
 	}
 	return state.success;
 }
@@ -453,7 +453,7 @@ LIBDCP_ENABLE_WARNINGS
 bool
 show_in_file_manager (boost::filesystem::path, boost::filesystem::path select)
 {
-	int r = system (String::compose("open -R \"%1\"", select.string()).c_str());
+	int r = system(fmt::format("open -R \"{}\"", select.string()).c_str());
 	return static_cast<bool>(WEXITSTATUS(r));
 }
 
diff --git a/src/lib/cross_windows.cc b/src/lib/cross_windows.cc
index 56ff73ec9..d4b8fe461 100644
--- a/src/lib/cross_windows.cc
+++ b/src/lib/cross_windows.cc
@@ -22,7 +22,6 @@
 #define UNICODE 1
 
 #include "cross.h"
-#include "compose.hpp"
 #include "log.h"
 #include "dcpomatic_log.h"
 #include "config.h"
@@ -404,7 +403,7 @@ get_device_number (HDEVINFO device_info, SP_DEVINFO_DATA* device_info_data)
 
 	auto r = SetupDiEnumDeviceInterfaces (device_info, device_info_data, &GUID_DEVICE_INTERFACE_DISK, 0, &device_interface_data);
 	if (!r) {
-		LOG_DISK("SetupDiEnumDeviceInterfaces failed (%1)", GetLastError());
+		LOG_DISK("SetupDiEnumDeviceInterfaces failed ({})", GetLastError());
 		return optional<int>();
 	}
 
@@ -439,7 +438,7 @@ get_device_number (HDEVINFO device_info, SP_DEVINFO_DATA* device_info_data)
 	free (device_detail_data);
 
 	if (device == INVALID_HANDLE_VALUE) {
-		LOG_DISK("CreateFileW failed with %1", GetLastError());
+		LOG_DISK("CreateFileW failed with {}", GetLastError());
 		return optional<int>();
 	}
 
@@ -469,7 +468,7 @@ typedef map<int, vector<boost::filesystem::path>> MountPoints;
 static void
 add_volume_mount_points (wchar_t* volume, MountPoints& mount_points)
 {
-	LOG_DISK("Looking at %1", wchar_to_utf8(volume));
+	LOG_DISK("Looking at {}", wchar_to_utf8(volume));
 
 	wchar_t volume_path_names[512];
 	vector<boost::filesystem::path> mp;
@@ -478,7 +477,7 @@ add_volume_mount_points (wchar_t* volume, MountPoints& mount_points)
 		wchar_t* p = volume_path_names;
 		while (*p != L'\0') {
 			mp.push_back (wchar_to_utf8(p));
-			LOG_DISK ("Found mount point %1", wchar_to_utf8(p));
+			LOG_DISK ("Found mount point {}", wchar_to_utf8(p));
 			p += wcslen(p) + 1;
 		}
 	}
@@ -555,7 +554,7 @@ Drive::get ()
 		if (!SetupDiEnumDeviceInfo(device_info, i, &device_info_data)) {
 			DWORD e = GetLastError();
 			if (e != ERROR_NO_MORE_ITEMS) {
-				LOG_DISK ("SetupDiEnumDeviceInfo failed (%1)", GetLastError());
+				LOG_DISK ("SetupDiEnumDeviceInfo failed ({})", GetLastError());
 			}
 			break;
 		}
@@ -567,7 +566,7 @@ Drive::get ()
 			continue;
 		}
 
-		string const physical_drive = String::compose("\\\\.\\PHYSICALDRIVE%1", *device_number);
+		string const physical_drive = fmt::format("\\\\.\\PHYSICALDRIVE{}", *device_number);
 
 		HANDLE device = CreateFileA (
 				physical_drive.c_str(), 0,
@@ -587,7 +586,7 @@ Drive::get ()
 				&geom, sizeof(geom), &returned, 0
 				);
 
-		LOG_DISK("Having a look through %1 locked volumes", locked_volumes.size());
+		LOG_DISK("Having a look through {} locked volumes", locked_volumes.size());
 		bool locked = false;
 		for (auto const& i: locked_volumes) {
 			if (i.second == physical_drive) {
@@ -598,7 +597,7 @@ Drive::get ()
 		if (r) {
 			uint64_t const disk_size = geom.Cylinders.QuadPart * geom.TracksPerCylinder * geom.SectorsPerTrack * geom.BytesPerSector;
 			drives.push_back (Drive(physical_drive, locked ? vector<boost::filesystem::path>() : mount_points[*device_number], disk_size, friendly_name, optional<string>()));
-			LOG_DISK("Added drive %1%2", drives.back().log_summary(), locked ? "(locked by us)" : "");
+			LOG_DISK("Added drive {}{}", drives.back().log_summary(), locked ? "(locked by us)" : "");
 		}
 
 		CloseHandle (device);
@@ -611,24 +610,24 @@ Drive::get ()
 bool
 Drive::unmount ()
 {
-	LOG_DISK("Unmounting %1 with %2 mount points", _device, _mount_points.size());
+	LOG_DISK("Unmounting {} with {} mount points", _device, _mount_points.size());
 	DCPOMATIC_ASSERT (_mount_points.size() == 1);
-	string const device_name = String::compose ("\\\\.\\%1", _mount_points.front());
-	string const truncated = device_name.substr (0, device_name.length() - 1);
-	LOG_DISK("Actually opening %1", truncated);
+	auto const device_name = fmt::format("\\\\.\\{}", _mount_points.front());
+	auto const truncated = device_name.substr(0, device_name.length() - 1);
+	LOG_DISK("Actually opening {}", truncated);
 	HANDLE device = CreateFileA (truncated.c_str(), (GENERIC_READ | GENERIC_WRITE), FILE_SHARE_READ | FILE_SHARE_WRITE, 0, OPEN_EXISTING, 0, 0);
  	if (device == INVALID_HANDLE_VALUE) {
-		LOG_DISK("Could not open %1 for unmount (%2)", truncated, GetLastError());
+		LOG_DISK("Could not open {} for unmount ({})", truncated, GetLastError());
 		return false;
 	}
 	DWORD returned;
 	BOOL r = DeviceIoControl (device, FSCTL_LOCK_VOLUME, 0, 0, 0, 0, &returned, 0);
 	if (!r) {
-		LOG_DISK("Unmount of %1 failed (%2)", truncated, GetLastError());
+		LOG_DISK("Unmount of {} failed ({})", truncated, GetLastError());
 		return false;
 	}
 
-	LOG_DISK("Unmount of %1 succeeded", _device);
+	LOG_DISK("Unmount of {} succeeded", _device);
 	locked_volumes.push_back (make_pair(device, _device));
 
 	return true;
@@ -660,7 +659,7 @@ disk_write_finished ()
 string
 dcpomatic::get_process_id ()
 {
-	return dcp::fmt::to_string(GetCurrentProcessId());
+	return fmt::to_string(GetCurrentProcessId());
 }
 
 
diff --git a/src/lib/curl_uploader.cc b/src/lib/curl_uploader.cc
index 389a5d6de..04a7e9273 100644
--- a/src/lib/curl_uploader.cc
+++ b/src/lib/curl_uploader.cc
@@ -24,7 +24,6 @@
 #include "exceptions.h"
 #include "config.h"
 #include "cross.h"
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
 #include <iostream>
 
@@ -94,12 +93,12 @@ CurlUploader::upload_file (boost::filesystem::path from, boost::filesystem::path
 	curl_easy_setopt (
 		_curl, CURLOPT_URL,
 		/* Use generic_string so that we get forward-slashes in the path, even on Windows */
-		String::compose ("ftp://%1/%2/%3", Config::instance()->tms_ip(), Config::instance()->tms_path(), to.generic_string ()).c_str ()
+		fmt::format("ftp://{}/{}/{}", Config::instance()->tms_ip(), Config::instance()->tms_path(), to.generic_string ()).c_str ()
 		);
 
 	dcp::File file(from, "rb");
 	if (!file) {
-		throw NetworkError (String::compose (_("Could not open %1 to send"), from));
+		throw NetworkError(fmt::format(_("Could not open {} to send"), from.string()));
 	}
 	_file = file.get();
 	_transferred = &transferred;
@@ -107,7 +106,7 @@ CurlUploader::upload_file (boost::filesystem::path from, boost::filesystem::path
 
 	auto const r = curl_easy_perform (_curl);
 	if (r != CURLE_OK) {
-		throw NetworkError (String::compose (_("Could not write to remote file (%1)"), curl_easy_strerror (r)));
+		throw NetworkError(fmt::format(_("Could not write to remote file ({})"), curl_easy_strerror(r)));
 	}
 
 	_file = nullptr;
@@ -133,7 +132,7 @@ int
 CurlUploader::debug(CURL *, curl_infotype type, char* data, size_t size)
 {
 	if (type == CURLINFO_TEXT && size > 0) {
-		LOG_GENERAL("CurlUploader: %1", string(data, size - 1));
+		LOG_GENERAL("CurlUploader: {}", string(data, size - 1));
 	}
 	return 0;
 }
diff --git a/src/lib/dcp_content.cc b/src/lib/dcp_content.cc
index 5e30dfc18..1400f8361 100644
--- a/src/lib/dcp_content.cc
+++ b/src/lib/dcp_content.cc
@@ -21,7 +21,6 @@
 
 #include "atmos_content.h"
 #include "audio_content.h"
-#include "compose.hpp"
 #include "config.h"
 #include "dcp_content.h"
 #include "dcp_decoder.h"
@@ -84,7 +83,7 @@ DCPContent::DCPContent (boost::filesystem::path p)
 	, _reference_audio (false)
 	, _three_d (false)
 {
-	LOG_GENERAL ("Creating DCP content from %1", p.string());
+	LOG_GENERAL ("Creating DCP content from {}", p.string());
 
 	read_directory (p);
 	set_default_colour_conversion ();
@@ -209,21 +208,21 @@ DCPContent::read_sub_directory (boost::filesystem::path p)
 {
 	using namespace boost::filesystem;
 
-	LOG_GENERAL ("DCPContent::read_sub_directory reads %1", p.string());
+	LOG_GENERAL ("DCPContent::read_sub_directory reads {}", p.string());
 	try {
 		for (auto i: directory_iterator(p)) {
 			if (is_regular_file(i.path())) {
-				LOG_GENERAL ("Inside there's regular file %1", i.path().string());
+				LOG_GENERAL ("Inside there's regular file {}", i.path().string());
 				add_path (i.path());
 			} else if (is_directory(i.path()) && i.path().filename() != ".AppleDouble") {
-				LOG_GENERAL ("Inside there's directory %1", i.path().string());
+				LOG_GENERAL ("Inside there's directory {}", i.path().string());
 				read_sub_directory (i.path());
 			} else {
-				LOG_GENERAL("Ignoring %1 from inside: status is %2", i.path().string(), static_cast<int>(status(i.path()).type()));
+				LOG_GENERAL("Ignoring {} from inside: status is {}", i.path().string(), static_cast<int>(status(i.path()).type()));
 			}
 		}
 	} catch (exception& e) {
-		LOG_GENERAL("Failed to iterate over %1: %2", p.string(), e.what());
+		LOG_GENERAL("Failed to iterate over {}: {}", p.string(), e.what());
 	}
 }
 
@@ -359,7 +358,7 @@ string
 DCPContent::summary () const
 {
 	boost::mutex::scoped_lock lm (_mutex);
-	return String::compose (_("%1 [DCP]"), _name);
+	return fmt::format(_("{} [DCP]"), _name);
 }
 
 string
@@ -751,7 +750,7 @@ DCPContent::can_reference_audio (shared_ptr<const Film> film, string& why_not) c
 	if (audio && audio->stream()) {
 		auto const channels = audio->stream()->channels();
 		if (channels != film->audio_channels()) {
-			why_not = String::compose(_("it has a different number of audio channels than the project; set the project to have %1 channels."), channels);
+			why_not = fmt::format(_("it has a different number of audio channels than the project; set the project to have {} channels."), channels);
 			return false;
 		}
 	}
diff --git a/src/lib/dcp_examiner.cc b/src/lib/dcp_examiner.cc
index 3ee6dd99c..8b2d60f8e 100644
--- a/src/lib/dcp_examiner.cc
+++ b/src/lib/dcp_examiner.cc
@@ -122,7 +122,7 @@ DCPExaminer::DCPExaminer (shared_ptr<const DCPContent> content, bool tolerant)
 	_name = selected_cpl->content_title_text();
 	_content_kind = selected_cpl->content_kind();
 
-	LOG_GENERAL ("Selected CPL %1", _cpl);
+	LOG_GENERAL("Selected CPL {}", _cpl);
 
 	auto try_to_parse_language = [](optional<string> lang) -> boost::optional<dcp::LanguageTag> {
 		try {
@@ -133,11 +133,11 @@ DCPExaminer::DCPExaminer (shared_ptr<const DCPContent> content, bool tolerant)
 		return boost::none;
 	};
 
-	LOG_GENERAL("Looking at %1 reels", selected_cpl->reels().size());
+	LOG_GENERAL("Looking at {} reels", selected_cpl->reels().size());
 
 	int reel_index = 0;
 	for (auto reel: selected_cpl->reels()) {
-		LOG_GENERAL("Reel %1", reel->id());
+		LOG_GENERAL("Reel {}", reel->id());
 
 		if (reel->main_picture()) {
 			/* This will mean a VF can be displayed in the timeline even if its picture asset
@@ -147,10 +147,10 @@ DCPExaminer::DCPExaminer (shared_ptr<const DCPContent> content, bool tolerant)
 			_video_length += reel->main_picture()->actual_duration();
 
 			if (!reel->main_picture()->asset_ref().resolved()) {
-				LOG_GENERAL("Main picture %1 of reel %2 is missing", reel->main_picture()->id(), reel->id());
+				LOG_GENERAL("Main picture {} of reel {} is missing", reel->main_picture()->id(), reel->id());
 				_needs_assets = true;
 			} else {
-				LOG_GENERAL("Main picture %1 of reel %2 found", reel->main_picture()->id(), reel->id());
+				LOG_GENERAL("Main picture {} of reel {} found", reel->main_picture()->id(), reel->id());
 
 				auto const frac = reel->main_picture()->edit_rate();
 				float const fr = float(frac.numerator) / frac.denominator;
@@ -178,10 +178,10 @@ DCPExaminer::DCPExaminer (shared_ptr<const DCPContent> content, bool tolerant)
 			auto const edit_rate = reel->main_sound()->edit_rate();
 
 			if (!reel->main_sound()->asset_ref().resolved()) {
-				LOG_GENERAL("Main sound %1 of reel %2 is missing", reel->main_sound()->id(), reel->id());
+				LOG_GENERAL("Main sound {} of reel {} is missing", reel->main_sound()->id(), reel->id());
 				_needs_assets = true;
 			} else {
-				LOG_GENERAL("Main sound %1 of reel %2 found", reel->main_sound()->id(), reel->id());
+				LOG_GENERAL("Main sound {} of reel {} found", reel->main_sound()->id(), reel->id());
 
 				auto asset = reel->main_sound()->asset();
 
@@ -213,10 +213,10 @@ DCPExaminer::DCPExaminer (shared_ptr<const DCPContent> content, bool tolerant)
 					_has_non_zero_entry_point[type] = true;
 				}
 				if (!reel_asset->asset_ref().resolved()) {
-					LOG_GENERAL("Main %1 %2 of reel %3 is missing", name, reel_asset->id(), reel->id());
+					LOG_GENERAL("Main {} {} of reel {} is missing", name, reel_asset->id(), reel->id());
 					_needs_assets = true;
 				} else {
-					LOG_GENERAL("Main %1 %2 of reel %3 found", name, reel_asset->id(), reel->id());
+					LOG_GENERAL("Main {} {} of reel {} found", name, reel_asset->id(), reel->id());
 
 					_text_count[type] = 1;
 					language = try_to_parse_language(reel_asset->language());
@@ -255,10 +255,10 @@ DCPExaminer::DCPExaminer (shared_ptr<const DCPContent> content, bool tolerant)
 					_has_non_zero_entry_point[type] = true;
 				}
 				if (!text->asset_ref().resolved()) {
-					LOG_GENERAL("Closed %1 %2 of reel %3 is missing", name, text->id(), reel->id());
+					LOG_GENERAL("Closed {} {} of reel {} is missing", name, text->id(), reel->id());
 					_needs_assets = true;
 				} else {
-					LOG_GENERAL("Closed %1 %2 of reel %3 found", name, text->id(), reel->id());
+					LOG_GENERAL("Closed {} {} of reel {} found", name, text->id(), reel->id());
 
 					auto asset = text->asset();
 					for (auto const& font: asset->font_data()) {
@@ -316,7 +316,7 @@ DCPExaminer::DCPExaminer (shared_ptr<const DCPContent> content, bool tolerant)
 	 */
 	try {
 		for (auto i: selected_cpl->reels()) {
-			LOG_GENERAL ("Reel %1", i->id());
+			LOG_GENERAL("Reel {}", i->id());
 			if (i->main_picture() && i->main_picture()->asset_ref().resolved()) {
 				auto pic = i->main_picture()->asset();
 				if (pic->encrypted() && !pic->key()) {
@@ -396,10 +396,10 @@ DCPExaminer::DCPExaminer (shared_ptr<const DCPContent> content, bool tolerant)
 		}
 	} catch (dcp::ReadError& e) {
 		_kdm_valid = false;
-		LOG_GENERAL ("KDM is invalid: %1", e.what());
+		LOG_GENERAL("KDM is invalid: {}", e.what());
 	} catch (dcp::MiscError& e) {
 		_kdm_valid = false;
-		LOG_GENERAL ("KDM is invalid: %1", e.what());
+		LOG_GENERAL("KDM is invalid: {}", e.what());
 	}
 
 	_standard = selected_cpl->standard();
diff --git a/src/lib/dcp_subtitle.cc b/src/lib/dcp_subtitle.cc
index c2d390b55..f43208b5d 100644
--- a/src/lib/dcp_subtitle.cc
+++ b/src/lib/dcp_subtitle.cc
@@ -21,9 +21,9 @@
 
 #include "dcp_subtitle.h"
 #include "exceptions.h"
-#include "compose.hpp"
 #include <dcp/interop_text_asset.h>
 #include <dcp/smpte_text_asset.h>
+#include <fmt/format.h>
 #include <memory>
 
 #include "i18n.h"
@@ -57,7 +57,7 @@ DCPSubtitle::load (boost::filesystem::path file) const
 	}
 
 	if (!sc) {
-		throw FileError(String::compose(_("Could not read subtitles (%1 / %2)"), interop_error, smpte_error), file);
+		throw FileError(fmt::format(_("Could not read subtitles ({} / {})"), interop_error, smpte_error), file);
 	}
 
 	return sc;
diff --git a/src/lib/dcp_text_track.cc b/src/lib/dcp_text_track.cc
index 292932396..4f93c8e23 100644
--- a/src/lib/dcp_text_track.cc
+++ b/src/lib/dcp_text_track.cc
@@ -20,7 +20,7 @@
 
 
 #include "dcp_text_track.h"
-#include "compose.hpp"
+#include <fmt/format.h>
 #include <string>
 
 #include "i18n.h"
@@ -50,7 +50,7 @@ DCPTextTrack::DCPTextTrack (string name_, optional<dcp::LanguageTag> language_)
 string
 DCPTextTrack::summary () const
 {
-	return String::compose("%1 (%2)", name, language ? language->to_string() : _("Unknown"));
+	return fmt::format("{} ({})", name, language ? language->to_string() : _("Unknown"));
 }
 
 void
diff --git a/src/lib/dcp_video.cc b/src/lib/dcp_video.cc
index f250d4505..cfcb62216 100644
--- a/src/lib/dcp_video.cc
+++ b/src/lib/dcp_video.cc
@@ -30,7 +30,6 @@
  */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "cross.h"
 #include "dcp_video.h"
@@ -151,7 +150,7 @@ DCPVideo::encode_locally () const
 	ArrayData enc = {};
 	/* This was empirically derived by a user: see #1902 */
 	int const minimum_size = 16384;
-	LOG_DEBUG_ENCODE("Using minimum frame size %1", minimum_size);
+	LOG_DEBUG_ENCODE("Using minimum frame size {}", minimum_size);
 
 	auto xyz = convert_to_xyz(_frame);
 	int noise_amount = 2;
@@ -167,11 +166,11 @@ DCPVideo::encode_locally () const
 		);
 
 		if (enc.size() >= minimum_size) {
-			LOG_DEBUG_ENCODE(N_("Frame %1 encoded size was OK (%2)"), _index, enc.size());
+			LOG_DEBUG_ENCODE(N_("Frame {} encoded size was OK ({})"), _index, enc.size());
 			break;
 		}
 
-		LOG_GENERAL (N_("Frame %1 encoded size was small (%2); adding noise at level %3 with pixel skip %4"), _index, enc.size(), noise_amount, pixel_skip);
+		LOG_GENERAL(N_("Frame {} encoded size was small ({}); adding noise at level {} with pixel skip {}"), _index, enc.size(), noise_amount, pixel_skip);
 
 		/* The JPEG2000 is too low-bitrate for some decoders <cough>DSS200</cough> so add some noise
 		 * and try again.  This is slow but hopefully won't happen too often.  We have to do
@@ -202,13 +201,13 @@ DCPVideo::encode_locally () const
 
 	switch (_frame->eyes()) {
 	case Eyes::BOTH:
-		LOG_DEBUG_ENCODE (N_("Finished locally-encoded frame %1 for mono"), _index);
+		LOG_DEBUG_ENCODE(N_("Finished locally-encoded frame {} for mono"), _index);
 		break;
 	case Eyes::LEFT:
-		LOG_DEBUG_ENCODE (N_("Finished locally-encoded frame %1 for L"), _index);
+		LOG_DEBUG_ENCODE(N_("Finished locally-encoded frame {} for L"), _index);
 		break;
 	case Eyes::RIGHT:
-		LOG_DEBUG_ENCODE (N_("Finished locally-encoded frame %1 for R"), _index);
+		LOG_DEBUG_ENCODE(N_("Finished locally-encoded frame {} for R"), _index);
 		break;
 	default:
 		break;
@@ -241,7 +240,7 @@ DCPVideo::encode_remotely (EncodeServerDescription serv, int timeout) const
 	cxml::add_text_child(root, "Version", fmt::to_string(SERVER_LINK_VERSION));
 	add_metadata (root);
 
-	LOG_DEBUG_ENCODE (N_("Sending frame %1 to remote"), _index);
+	LOG_DEBUG_ENCODE(N_("Sending frame {} to remote"), _index);
 
 	{
 		Socket::WriteDigestScope ds (socket);
@@ -252,7 +251,7 @@ DCPVideo::encode_remotely (EncodeServerDescription serv, int timeout) const
 		socket->write ((uint8_t *) xml.c_str(), xml.bytes() + 1);
 
 		/* Send binary data */
-		LOG_TIMING("start-remote-send thread=%1", thread_id ());
+		LOG_TIMING("start-remote-send thread={}", thread_id ());
 		_frame->write_to_socket (socket);
 	}
 
@@ -260,16 +259,16 @@ DCPVideo::encode_remotely (EncodeServerDescription serv, int timeout) const
 	   is ready and sent back.
 	*/
 	Socket::ReadDigestScope ds (socket);
-	LOG_TIMING("start-remote-encode thread=%1", thread_id ());
+	LOG_TIMING("start-remote-encode thread={}", thread_id ());
 	ArrayData e (socket->read_uint32 ());
-	LOG_TIMING("start-remote-receive thread=%1", thread_id ());
+	LOG_TIMING("start-remote-receive thread={}", thread_id ());
 	socket->read (e.data(), e.size());
-	LOG_TIMING("finish-remote-receive thread=%1", thread_id ());
+	LOG_TIMING("finish-remote-receive thread={}", thread_id ());
 	if (!ds.check()) {
 		throw NetworkError ("Checksums do not match");
 	}
 
-	LOG_DEBUG_ENCODE (N_("Finished remotely-encoded frame %1"), _index);
+	LOG_DEBUG_ENCODE(N_("Finished remotely-encoded frame {}"), _index);
 
 	return e;
 }
diff --git a/src/lib/dcpomatic_log.h b/src/lib/dcpomatic_log.h
index 2372c8d01..237f5e5d0 100644
--- a/src/lib/dcpomatic_log.h
+++ b/src/lib/dcpomatic_log.h
@@ -20,30 +20,30 @@
 
 
 #include "log.h"
-#include "compose.hpp"
+#include <fmt/format.h>
 
 
 /** The current log; set up by the front-ends when they have a Film to log into */
 extern std::shared_ptr<Log> dcpomatic_log;
 
 
-#define LOG_GENERAL(...)      dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_GENERAL);
+#define LOG_GENERAL(...)      dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_GENERAL);
 #define LOG_GENERAL_NC(...)   dcpomatic_log->log(__VA_ARGS__, LogEntry::TYPE_GENERAL);
-#define LOG_ERROR(...)        dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_ERROR);
+#define LOG_ERROR(...)        dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_ERROR);
 #define LOG_ERROR_NC(...)     dcpomatic_log->log(__VA_ARGS__, LogEntry::TYPE_ERROR);
-#define LOG_WARNING(...)      dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_WARNING);
+#define LOG_WARNING(...)      dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_WARNING);
 #define LOG_WARNING_NC(...)   dcpomatic_log->log(__VA_ARGS__, LogEntry::TYPE_WARNING);
-#define LOG_TIMING(...)       dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_TIMING);
-#define LOG_DEBUG_ENCODE(...) dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_DEBUG_ENCODE);
-#define LOG_DEBUG_VIDEO_VIEW(...) dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_DEBUG_VIDEO_VIEW);
-#define LOG_DEBUG_THREE_D(...) dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_DEBUG_THREE_D);
+#define LOG_TIMING(...)       dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_TIMING);
+#define LOG_DEBUG_ENCODE(...) dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_DEBUG_ENCODE);
+#define LOG_DEBUG_VIDEO_VIEW(...) dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_DEBUG_VIDEO_VIEW);
+#define LOG_DEBUG_THREE_D(...) dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_DEBUG_THREE_D);
 #define LOG_DEBUG_THREE_D_NC(...) dcpomatic_log->log(__VA_ARGS__, LogEntry::TYPE_DEBUG_THREE_D);
-#define LOG_DISK(...)         dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_DISK);
+#define LOG_DISK(...)         dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_DISK);
 #define LOG_DISK_NC(...)      dcpomatic_log->log(__VA_ARGS__, LogEntry::TYPE_DISK);
-#define LOG_DEBUG_PLAYER(...)    dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_DEBUG_PLAYER);
+#define LOG_DEBUG_PLAYER(...)    dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_DEBUG_PLAYER);
 #define LOG_DEBUG_PLAYER_NC(...) dcpomatic_log->log(__VA_ARGS__, LogEntry::TYPE_DEBUG_PLAYER);
-#define LOG_DEBUG_AUDIO_ANALYSIS(...)    dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_DEBUG_AUDIO_ANALYSIS);
+#define LOG_DEBUG_AUDIO_ANALYSIS(...)    dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_DEBUG_AUDIO_ANALYSIS);
 #define LOG_DEBUG_AUDIO_ANALYSIS_NC(...) dcpomatic_log->log(__VA_ARGS__, LogEntry::TYPE_DEBUG_AUDIO_ANALYSIS);
-#define LOG_HTTP(...)         dcpomatic_log->log(String::compose(__VA_ARGS__), LogEntry::TYPE_HTTP);
+#define LOG_HTTP(...)         dcpomatic_log->log(fmt::format(__VA_ARGS__), LogEntry::TYPE_HTTP);
 #define LOG_HTTP_NC(...)      dcpomatic_log->log(__VA_ARGS__, LogEntry::TYPE_HTTP);
 
diff --git a/src/lib/dcpomatic_socket.cc b/src/lib/dcpomatic_socket.cc
index 83ab072d2..0d3879755 100644
--- a/src/lib/dcpomatic_socket.cc
+++ b/src/lib/dcpomatic_socket.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
 #include "dcpomatic_log.h"
 #include "dcpomatic_socket.h"
@@ -71,7 +70,7 @@ Socket::connect (boost::asio::ip::tcp::endpoint endpoint)
 	} while (ec == boost::asio::error::would_block);
 
 	if (ec) {
-		throw NetworkError (String::compose (_("error during async_connect (%1)"), ec.value ()));
+		throw NetworkError(fmt::format(_("error during async_connect ({})"), ec.value ()));
 	}
 
 	if (!_socket.is_open ()) {
@@ -105,7 +104,7 @@ Socket::write (uint8_t const * data, int size)
 	} while (ec == boost::asio::error::would_block);
 
 	if (ec) {
-		throw NetworkError (String::compose (_("error during async_write (%1)"), ec.value ()));
+		throw NetworkError(fmt::format(_("error during async_write ({})"), ec.value()));
 	}
 
 	if (_write_digester) {
@@ -146,7 +145,7 @@ Socket::read (uint8_t* data, int size)
 	} while (ec == boost::asio::error::would_block);
 
 	if (ec) {
-		throw NetworkError (String::compose (_("error during async_read (%1)"), ec.value ()));
+		throw NetworkError(fmt::format(_("error during async_read ({})"), ec.value()));
 	}
 
 	if (_read_digester) {
diff --git a/src/lib/disk_writer_messages.cc b/src/lib/disk_writer_messages.cc
index d12207dbf..562e9e876 100644
--- a/src/lib/disk_writer_messages.cc
+++ b/src/lib/disk_writer_messages.cc
@@ -72,25 +72,25 @@ DiskWriterBackEndResponse::write_to_nanomsg(Nanomsg& nanomsg, int timeout) const
 	switch (_type)
 	{
 		case Type::OK:
-			message = String::compose("%1\n", DISK_WRITER_OK);
+			message = fmt::format("{}\n", DISK_WRITER_OK);
 			break;
 		case Type::ERROR:
-			message = String::compose("%1\n%2\n%3\n%4\n", DISK_WRITER_ERROR, _error_message, _ext4_error_number, _platform_error_number);
+			message = fmt::format("{}\n{}\n{}\n{}\n", DISK_WRITER_ERROR, _error_message, _ext4_error_number, _platform_error_number);
 			break;
 		case Type::PONG:
-			message = String::compose("%1\n", DISK_WRITER_PONG);
+			message = fmt::format("{}\n", DISK_WRITER_PONG);
 			break;
 		case Type::FORMAT_PROGRESS:
-			message = String::compose("%1\n", DISK_WRITER_FORMAT_PROGRESS);
-			message += dcp::fmt::to_string(_progress) + "\n";
+			message = fmt::format("{}\n", DISK_WRITER_FORMAT_PROGRESS);
+			message += fmt::to_string(_progress) + "\n";
 			break;
 		case Type::COPY_PROGRESS:
-			message = String::compose("%1\n", DISK_WRITER_COPY_PROGRESS);
-			message += dcp::fmt::to_string(_progress) + "\n";
+			message = fmt::format("{}\n", DISK_WRITER_COPY_PROGRESS);
+			message += fmt::to_string(_progress) + "\n";
 			break;
 		case Type::VERIFY_PROGRESS:
-			message = String::compose("%1\n", DISK_WRITER_VERIFY_PROGRESS);
-			message += dcp::fmt::to_string(_progress) + "\n";
+			message = fmt::format("{}\n", DISK_WRITER_VERIFY_PROGRESS);
+			message += fmt::to_string(_progress) + "\n";
 			break;
 	}
 
diff --git a/src/lib/dkdm_wrapper.cc b/src/lib/dkdm_wrapper.cc
index 4c7838a8d..1effb6c4a 100644
--- a/src/lib/dkdm_wrapper.cc
+++ b/src/lib/dkdm_wrapper.cc
@@ -19,13 +19,13 @@
 */
 
 
-#include "compose.hpp"
 #include "dkdm_wrapper.h"
 #include "dcpomatic_assert.h"
 #include <dcp/warnings.h>
 LIBDCP_DISABLE_WARNINGS
 #include <libxml++/libxml++.h>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 
 
 using std::string;
@@ -61,7 +61,7 @@ DKDMBase::read (cxml::ConstNodePtr node)
 string
 DKDM::name () const
 {
-	return String::compose ("%1 (%2)", _dkdm.content_title_text(), _dkdm.cpl_id());
+	return fmt::format("{} ({})", _dkdm.content_title_text(), _dkdm.cpl_id());
 }
 
 
diff --git a/src/lib/email.cc b/src/lib/email.cc
index 7a6e58d91..10393945f 100644
--- a/src/lib/email.cc
+++ b/src/lib/email.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "email.h"
 #include "exceptions.h"
@@ -146,7 +145,7 @@ Email::send(string server, int port, EmailProtocol protocol, string user, string
 	}
 
 	_email += "Subject: " + encode_rfc1342(_subject) + "\r\n" +
-		variant::insert_dcpomatic("User-Agent: %1\r\n\r\n");
+		variant::insert_dcpomatic("User-Agent: {}\r\n\r\n");
 
 	if (!_attachments.empty ()) {
 		_email += "--" + boundary + "\r\n"
@@ -195,9 +194,9 @@ Email::send(string server, int port, EmailProtocol protocol, string user, string
 
 	if ((protocol == EmailProtocol::AUTO && port == 465) || protocol == EmailProtocol::SSL) {
 		/* "SSL" or "Implicit TLS"; I think curl wants us to use smtps here */
-		curl_easy_setopt (curl, CURLOPT_URL, String::compose("smtps://%1:%2", server, port).c_str());
+		curl_easy_setopt(curl, CURLOPT_URL, fmt::format("smtps://{}:{}", server, port).c_str());
 	} else {
-		curl_easy_setopt (curl, CURLOPT_URL, String::compose("smtp://%1:%2", server, port).c_str());
+		curl_easy_setopt(curl, CURLOPT_URL, fmt::format("smtp://{}:{}", server, port).c_str());
 	}
 
 	if (!user.empty ()) {
@@ -237,7 +236,7 @@ Email::send(string server, int port, EmailProtocol protocol, string user, string
 
 	auto const r = curl_easy_perform (curl);
 	if (r != CURLE_OK) {
-		throw NetworkError(_("Failed to send email"), String::compose("%1 sending to %2:%3", curl_easy_strerror(r), server, port));
+		throw NetworkError(_("Failed to send email"), fmt::format("{} sending to {}:{}", curl_easy_strerror(r), server, port));
 	}
 
 	curl_slist_free_all (recipients);
diff --git a/src/lib/encode_server.cc b/src/lib/encode_server.cc
index 08e661eac..4862e62cc 100644
--- a/src/lib/encode_server.cc
+++ b/src/lib/encode_server.cc
@@ -25,7 +25,6 @@
  */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "cross.h"
@@ -167,7 +166,7 @@ EncodeServer::process (shared_ptr<Socket> socket, struct timeval& after_read, st
 		socket->write (encoded.data(), encoded.size());
 	} catch (std::exception& e) {
 		cerr << "Send failed; frame " << dcp_video_frame.index() << "\n";
-		LOG_ERROR ("Send failed; frame %1", dcp_video_frame.index());
+		LOG_ERROR("Send failed; frame {}", dcp_video_frame.index());
 		throw;
 	}
 
@@ -210,7 +209,7 @@ EncodeServer::worker_thread ()
 			ip = socket->socket().remote_endpoint().address().to_string();
 		} catch (std::exception& e) {
 			cerr << "Error: " << e.what() << "\n";
-			LOG_ERROR ("Error: %1", e.what());
+			LOG_ERROR("Error: {}", e.what());
 		}
 
 		gettimeofday (&end, 0);
@@ -245,7 +244,7 @@ EncodeServer::worker_thread ()
 void
 EncodeServer::run ()
 {
-	LOG_GENERAL ("Server %1 (%2) starting with %3 threads", dcpomatic_version, dcpomatic_git_commit, _num_threads);
+	LOG_GENERAL("Server {} ({}) starting with {} threads", dcpomatic_version, dcpomatic_git_commit, _num_threads);
 	if (_verbose) {
 		cout << variant::dcpomatic_encode_server() << " starting with " << _num_threads << " threads.\n";
 	}
diff --git a/src/lib/encode_server_finder.cc b/src/lib/encode_server_finder.cc
index 22c1d37dd..2a20a61f1 100644
--- a/src/lib/encode_server_finder.cc
+++ b/src/lib/encode_server_finder.cc
@@ -189,7 +189,7 @@ try {
 			new tcp::acceptor (_listen_io_service, tcp::endpoint(tcp::v4(), is_batch_converter ? BATCH_SERVER_PRESENCE_PORT : MAIN_SERVER_PRESENCE_PORT))
 			);
 	} catch (...) {
-		boost::throw_exception(NetworkError(variant::insert_dcpomatic(_("Could not listen for remote encode servers.  Perhaps another instance of %1 is running."))));
+		boost::throw_exception(NetworkError(variant::insert_dcpomatic(_("Could not listen for remote encode servers.  Perhaps another instance of {} is running."))));
 	}
 
 	start_accept ();
diff --git a/src/lib/environment_info.cc b/src/lib/environment_info.cc
index d6592d126..503050870 100644
--- a/src/lib/environment_info.cc
+++ b/src/lib/environment_info.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "cross.h"
 #include "log.h"
 #include "variant.h"
@@ -36,6 +35,7 @@ extern "C" {
 #include <libavutil/pixfmt.h>
 }
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 #include <boost/thread.hpp>
 
 #include "i18n.h"
@@ -86,18 +86,18 @@ environment_info ()
 {
 	list<string> info;
 
-	info.push_back(String::compose("%1 %2 git %3 using %4", variant::dcpomatic(), dcpomatic_version, dcpomatic_git_commit, dependency_version_summary()));
+	info.push_back(fmt::format("{} {} git {} using {}", variant::dcpomatic(), dcpomatic_version, dcpomatic_git_commit, dependency_version_summary()));
 
 	{
 		char buffer[128];
 		gethostname (buffer, sizeof (buffer));
-		info.push_back (String::compose ("Host name %1", &buffer[0]));
+		info.push_back(fmt::format("Host name {}", &buffer[0]));
 	}
 
 #ifdef DCPOMATIC_DEBUG
-	info.push_back(variant::insert_dcpomatic("%1 built in debug mode."));
+	info.push_back(variant::insert_dcpomatic("{} built in debug mode."));
 #else
-	info.push_back(variant::insert_dcpomatic("%1 built in optimised mode."));
+	info.push_back(variant::insert_dcpomatic("{} built in optimised mode."));
 #endif
 #ifdef LIBDCP_DEBUG
 	info.push_back ("libdcp built in debug mode.");
@@ -110,8 +110,8 @@ environment_info ()
 	os_info.dwOSVersionInfoSize = sizeof (os_info);
 	GetVersionEx (&os_info);
 	info.push_back (
-		String::compose (
-			"Windows version %1.%2.%3",
+		fmt::format(
+			"Windows version {}.{}.{}",
 			(int) os_info.dwMajorVersion, (int) os_info.dwMinorVersion, (int) os_info.dwBuildNumber
 			)
 		);
@@ -142,9 +142,9 @@ environment_info ()
 #endif
 #endif
 
-	info.push_back (String::compose ("CPU: %1, %2 processors", cpu_info(), boost::thread::hardware_concurrency()));
+	info.push_back(fmt::format("CPU: {}, {} processors", cpu_info(), boost::thread::hardware_concurrency()));
 	for (auto const& i: mount_info()) {
-		info.push_back (String::compose("Mount: %1 %2", i.first, i.second));
+		info.push_back(fmt::format("Mount: {} {}", i.first, i.second));
 	}
 
 	return info;
diff --git a/src/lib/exceptions.cc b/src/lib/exceptions.cc
index 27496dcdc..ffdda2d6a 100644
--- a/src/lib/exceptions.cc
+++ b/src/lib/exceptions.cc
@@ -20,22 +20,22 @@
 
 
 #include "exceptions.h"
-#include "compose.hpp"
+#include <fmt/format.h>
 
 #include "i18n.h"
 
 
-using std::string;
 using std::runtime_error;
+using std::string;
 using boost::optional;
 
 
 /** @param f File that we were trying to open */
 OpenFileError::OpenFileError (boost::filesystem::path f, int error, Mode mode)
 	: FileError (
-		String::compose (
-			mode == READ_WRITE ? _("could not open file %1 for read/write (%2)") :
-			(mode == READ ? _("could not open file %1 for read (%2)") : _("could not open file %1 for write (%2)")),
+		fmt::format(
+			mode == READ_WRITE ? _("could not open file {} for read/write ({})") :
+			(mode == READ ? _("could not open file {} for read ({})") : _("could not open file {} for write ({})")),
 			f.string(),
 			error),
 		f
@@ -46,7 +46,7 @@ OpenFileError::OpenFileError (boost::filesystem::path f, int error, Mode mode)
 
 
 FileNotFoundError::FileNotFoundError (boost::filesystem::path f)
-	: runtime_error(String::compose("File %1 not found", f.string()))
+	: runtime_error(fmt::format("File {} not found", f.string()))
 	, _file (f)
 {
 
@@ -54,35 +54,35 @@ FileNotFoundError::FileNotFoundError (boost::filesystem::path f)
 
 
 ReadFileError::ReadFileError (boost::filesystem::path f, int e)
-	: FileError (String::compose(_("could not read from file %1 (%2)"), f.string(), strerror(e)), f)
+	: FileError(fmt::format(_("could not read from file {} ({})"), f.string(), strerror(e)), f)
 {
 
 }
 
 
 WriteFileError::WriteFileError (boost::filesystem::path f, int e)
-	: FileError (String::compose(_("could not write to file %1 (%2)"), f.string(), strerror(e)), f)
+	: FileError(fmt::format(_("could not write to file {} ({})"), f.string(), strerror(e)), f)
 {
 
 }
 
 
 MissingSettingError::MissingSettingError (string s)
-	: SettingError (s, String::compose(_("Missing required setting %1"), s))
+	: SettingError(s, fmt::format(_("Missing required setting {}"), s))
 {
 
 }
 
 
 PixelFormatError::PixelFormatError (string o, AVPixelFormat f)
-	: runtime_error (String::compose(_("Cannot handle pixel format %1 during %2"), (int) f, o))
+	: runtime_error(fmt::format(_("Cannot handle pixel format {} during {}"), (int) f, o))
 {
 
 }
 
 
 TextSubtitleError::TextSubtitleError (string saw, string expecting, boost::filesystem::path f)
-	: FileError (String::compose(_("Error in subtitle file: saw %1 while expecting %2"), saw.empty() ? "[nothing]" : saw, expecting), f)
+	: FileError(fmt::format(_("Error in subtitle file: saw {} while expecting {}"), saw.empty() ? "[nothing]" : saw, expecting), f)
 {
 
 }
@@ -96,14 +96,14 @@ InvalidSignerError::InvalidSignerError ()
 
 
 InvalidSignerError::InvalidSignerError (string reason)
-	: runtime_error (String::compose(_("The certificate chain for signing is invalid (%1)"), reason))
+	: runtime_error(fmt::format(_("The certificate chain for signing is invalid ({})"), reason))
 {
 
 }
 
 
 ProgrammingError::ProgrammingError (string file, int line, string message)
-	: runtime_error (String::compose(_("Programming error at %1:%2 %3"), file, line, message))
+	: runtime_error(fmt::format(_("Programming error at {}:{} {}"), file, line, message))
 {
 
 }
@@ -117,7 +117,7 @@ KDMAsContentError::KDMAsContentError ()
 
 
 NetworkError::NetworkError (string s, optional<string> d)
-	: runtime_error (String::compose("%1%2", s, d ? String::compose(" (%1)", *d) : ""))
+	: runtime_error(fmt::format("{}{}", s, d ? fmt::format(" ({})", *d) : ""))
 	, _summary (s)
 	, _detail (d)
 {
@@ -126,7 +126,7 @@ NetworkError::NetworkError (string s, optional<string> d)
 
 
 KDMError::KDMError (string s, string d)
-	: runtime_error (String::compose("%1 (%2)", s, d))
+	: runtime_error(fmt::format("{} ({})", s, d))
 	, _summary (s)
 	, _detail (d)
 {
@@ -135,7 +135,7 @@ KDMError::KDMError (string s, string d)
 
 
 GLError::GLError (char const* last, int e)
-	: runtime_error (String::compose("%1 failed %2", last, e))
+	: runtime_error(fmt::format("{} failed {}", last, e))
 {
 
 }
@@ -149,7 +149,7 @@ GLError::GLError (char const* message)
 
 
 CopyError::CopyError(string m, optional<int> ext4, optional<int> platform)
-	: runtime_error(String::compose("%1%2%3", m, ext4 ? String::compose(" (%1)", *ext4) : "", platform ? String::compose(" (%1)", *platform) : ""))
+	: runtime_error(fmt::format("{}{}{}", m, ext4 ? fmt::format(" ({})", *ext4) : "", platform ? fmt::format(" ({})", *platform) : ""))
 	, _message (m)
 	, _ext4_number(ext4)
 	, _platform_number(platform)
@@ -166,7 +166,7 @@ CommunicationFailedError::CommunicationFailedError ()
 
 
 VerifyError::VerifyError (string m, int n)
-	: runtime_error (String::compose("%1 (%2)", m, n))
+	: runtime_error(fmt::format("{} ({})", m, n))
 	, _message (m)
 	, _number (n)
 {
@@ -175,7 +175,7 @@ VerifyError::VerifyError (string m, int n)
 
 
 DiskFullError::DiskFullError(boost::filesystem::path writing)
-	: std::runtime_error(String::compose(_("Disk full when writing %1"), writing.string()))
+	: std::runtime_error(fmt::format(_("Disk full when writing {}"), writing.string()))
 {
 
 }
diff --git a/src/lib/exceptions.h b/src/lib/exceptions.h
index f7e9c9dc5..406ef8443 100644
--- a/src/lib/exceptions.h
+++ b/src/lib/exceptions.h
@@ -31,6 +31,7 @@
 extern "C" {
 #include <libavutil/pixfmt.h>
 }
+#include <fmt/format.h>
 #include <boost/filesystem.hpp>
 #include <boost/optional.hpp>
 #include <sqlite3.h>
@@ -50,19 +51,19 @@ public:
 	{}
 
 	DecodeError (std::string function, std::string caller)
-		: std::runtime_error (String::compose("%1 failed [%2]", function, caller))
+		: std::runtime_error(fmt::format("{} failed [{}]", function, caller))
 	{}
 
 	DecodeError (std::string function, std::string caller, int error)
-		: std::runtime_error (String::compose("%1 failed [%2] (%3)", function, caller, error))
+		: std::runtime_error(fmt::format("{} failed [{}] ({})", function, caller, error))
 	{}
 
 	DecodeError (std::string function, std::string caller, boost::filesystem::path file)
-		: std::runtime_error (String::compose("%1 failed [%2] (%3)", function, caller, file.string()))
+		: std::runtime_error(fmt::format("{} failed [{}] ({})", function, caller, file.string()))
 	{}
 
 	DecodeError (std::string function, std::string caller, int error, boost::filesystem::path file)
-		: std::runtime_error (String::compose("%1 failed [%2] (%3) (%4)", function, caller, error, file.string()))
+		: std::runtime_error(fmt::format("{} failed [{}] ({}) ({})", function, caller, error, file.string()))
 	{}
 };
 
@@ -86,12 +87,12 @@ public:
 		: std::runtime_error (s)
 	{}
 
-	explicit EncodeError (std::string function, std::string caller)
-		: std::runtime_error (String::compose("%1 failed [%2]", function, caller))
+	EncodeError(std::string function, std::string caller)
+		: std::runtime_error(fmt::format("{} failed [{}]", function, caller))
 	{}
 
-	explicit EncodeError (std::string function, std::string caller, int error)
-		: std::runtime_error (String::compose("%1 failed [%2] (%3)", function, caller, error))
+	EncodeError(std::string function, std::string caller, int error)
+		: std::runtime_error(fmt::format("{} failed [{}] ({})", function, caller, error))
 	{}
 };
 
@@ -106,7 +107,7 @@ public:
 	 *  @param f Name of the file that this exception concerns.
 	 */
 	FileError (std::string m, boost::filesystem::path f)
-		: std::runtime_error (String::compose("%1 with %2", m, f.string()))
+		: std::runtime_error(fmt::format("{} with {}", m, f.string()))
 		, _file (f)
 	{}
 
@@ -339,7 +340,7 @@ class CPLNotFoundError : public DCPError
 {
 public:
 	CPLNotFoundError(std::string id)
-		: DCPError(String::compose("CPL %1 not found", id))
+		: DCPError(fmt::format("CPL {} not found", id))
 	{}
 };
 
@@ -517,17 +518,17 @@ private:
 
 	std::string get_message(sqlite3* db, char const* s)
 	{
-		return String::compose("%1 (in %2)", s, get_filename(db));
+		return fmt::format("{} (in {})", s, get_filename(db).string());
 	}
 
 	std::string get_message(sqlite3* db, int rc)
 	{
-		return String::compose("%1 (in %2)", sqlite3_errstr(rc), get_filename(db));
+		return fmt::format("{} (in {})", sqlite3_errstr(rc), get_filename(db).string());
 	}
 
 	std::string get_message(sqlite3* db, int rc, std::string doing)
 	{
-		return String::compose("%1 (while doing %2) (in %3)", sqlite3_errstr(rc), doing, get_filename(db));
+		return fmt::format("{} (while doing {}) (in {})", sqlite3_errstr(rc), doing, get_filename(db).string());
 	}
 
 	boost::filesystem::path _filename;
diff --git a/src/lib/ext.cc b/src/lib/ext.cc
index 25946df73..ce32e0556 100644
--- a/src/lib/ext.cc
+++ b/src/lib/ext.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "cross.h"
 #include "dcpomatic_log.h"
 #include "digester.h"
@@ -114,13 +113,13 @@ write (boost::filesystem::path from, boost::filesystem::path to, uint64_t& total
 	ext4_file out;
 	int r = ext4_fopen(&out, to.generic_string().c_str(), "wb");
 	if (r != EOK) {
-		throw CopyError(String::compose("Failed to open file %1", to.generic_string()), r, ext4_blockdev_errno);
+		throw CopyError(fmt::format("Failed to open file {}", to.generic_string()), r, ext4_blockdev_errno);
 	}
 
 	dcp::File in(from, "rb");
 	if (!in) {
 		ext4_fclose (&out);
-		throw CopyError(String::compose("Failed to open file %1", from.string()), 0);
+		throw CopyError(fmt::format("Failed to open file {}", from.string()), 0);
 	}
 
 	std::vector<uint8_t> buffer(block_size);
@@ -134,7 +133,7 @@ write (boost::filesystem::path from, boost::filesystem::path to, uint64_t& total
 		size_t read = in.read(buffer.data(), 1, this_time);
 		if (read != this_time) {
 			ext4_fclose (&out);
-			throw CopyError(String::compose("Short read; expected %1 but read %2", this_time, read), 0, ext4_blockdev_errno);
+			throw CopyError(fmt::format("Short read; expected {} but read {}", this_time, read), 0, ext4_blockdev_errno);
 		}
 
 		digester.add (buffer.data(), this_time);
@@ -147,7 +146,7 @@ write (boost::filesystem::path from, boost::filesystem::path to, uint64_t& total
 		}
 		if (written != this_time) {
 			ext4_fclose (&out);
-			throw CopyError(String::compose("Short write; expected %1 but wrote %2", this_time, written), 0, ext4_blockdev_errno);
+			throw CopyError(fmt::format("Short write; expected {} but wrote {}", this_time, written), 0, ext4_blockdev_errno);
 		}
 		remaining -= this_time;
 		total_remaining -= this_time;
@@ -171,12 +170,12 @@ string
 read (boost::filesystem::path from, boost::filesystem::path to, uint64_t& total_remaining, uint64_t total, Nanomsg* nanomsg)
 {
 	ext4_file in;
-	LOG_DISK("Opening %1 for read", to.generic_string());
+	LOG_DISK("Opening {} for read", to.generic_string());
 	int r = ext4_fopen(&in, to.generic_string().c_str(), "rb");
 	if (r != EOK) {
-		throw VerifyError (String::compose("Failed to open file %1", to.generic_string()), r);
+		throw VerifyError(fmt::format("Failed to open file {}", to.generic_string()), r);
 	}
-	LOG_DISK("Opened %1 for read", to.generic_string());
+	LOG_DISK("Opened {} for read", to.generic_string());
 
 	std::vector<uint8_t> buffer(block_size);
 	Digester digester;
@@ -188,7 +187,7 @@ read (boost::filesystem::path from, boost::filesystem::path to, uint64_t& total_
 		r = ext4_fread (&in, buffer.data(), this_time, &read);
 		if (read != this_time) {
 			ext4_fclose (&in);
-			throw VerifyError (String::compose("Short read; expected %1 but read %2", this_time, read), 0);
+			throw VerifyError(fmt::format("Short read; expected {} but read {}", this_time, read), 0);
 		}
 
 		digester.add (buffer.data(), this_time);
@@ -228,7 +227,7 @@ static
 void
 copy (boost::filesystem::path from, boost::filesystem::path to, uint64_t& total_remaining, uint64_t total, vector<CopiedFile>& copied_files, Nanomsg* nanomsg)
 {
-	LOG_DISK ("Copy %1 -> %2", from.string(), to.generic_string());
+	LOG_DISK("Copy {} -> {}", from.string(), to.generic_string());
 	from = dcp::filesystem::fix_long_path(from);
 
 	using namespace boost::filesystem;
@@ -238,7 +237,7 @@ copy (boost::filesystem::path from, boost::filesystem::path to, uint64_t& total_
 	if (is_directory(from)) {
 		int r = ext4_dir_mk (cr.generic_string().c_str());
 		if (r != EOK) {
-			throw CopyError(String::compose("Failed to create directory %1", cr.generic_string()), r, ext4_blockdev_errno);
+			throw CopyError(fmt::format("Failed to create directory {}", cr.generic_string()), r, ext4_blockdev_errno);
 		}
 		set_timestamps_to_now (cr);
 
@@ -247,7 +246,7 @@ copy (boost::filesystem::path from, boost::filesystem::path to, uint64_t& total_
 		}
 	} else {
 		string const write_digest = write (from, cr, total_remaining, total, nanomsg);
-		LOG_DISK ("Wrote %1 %2 with %3", from.string(), cr.generic_string(), write_digest);
+		LOG_DISK("Wrote {} {} with {}", from.string(), cr.generic_string(), write_digest);
 		copied_files.push_back (CopiedFile(from, cr, write_digest));
 	}
 }
@@ -260,7 +259,7 @@ verify (vector<CopiedFile> const& copied_files, uint64_t total, Nanomsg* nanomsg
 	uint64_t total_remaining = total;
 	for (auto const& i: copied_files) {
 		string const read_digest = read (i.from, i.to, total_remaining, total, nanomsg);
-		LOG_DISK ("Read %1 %2 was %3 on write, now %4", i.from.string(), i.to.generic_string(), i.write_digest, read_digest);
+		LOG_DISK("Read {} {} was {} on write, now {}", i.from.string(), i.to.generic_string(), i.write_digest, read_digest);
 		if (read_digest != i.write_digest) {
 			throw VerifyError ("Hash of written data is incorrect", 0);
 		}
@@ -348,7 +347,7 @@ try
 	close(fd);
 #endif
 
-	LOG_DISK ("Writing to partition at %1 size %2; bd part size is %3", bdevs.partitions[0].part_offset, bdevs.partitions[0].part_size, bd->part_size);
+	LOG_DISK("Writing to partition at {} size {}; bd part size is {}", bdevs.partitions[0].part_offset, bdevs.partitions[0].part_size, bd->part_size);
 
 #ifdef DCPOMATIC_WINDOWS
 	file_windows_partition_set (bdevs.partitions[0].part_offset, bdevs.partitions[0].part_size);
@@ -426,17 +425,17 @@ try
 
 	disk_write_finished ();
 } catch (CopyError& e) {
-	LOG_DISK("CopyError (from write): %1 %2 %3", e.message(), e.ext4_number().get_value_or(0), e.platform_number().get_value_or(0));
+	LOG_DISK("CopyError (from write): {} {} {}", e.message(), e.ext4_number().get_value_or(0), e.platform_number().get_value_or(0));
 	if (nanomsg) {
 		DiskWriterBackEndResponse::error(e.message(), e.ext4_number().get_value_or(0), e.platform_number().get_value_or(0)).write_to_nanomsg(*nanomsg, LONG_TIMEOUT);
 	}
 } catch (VerifyError& e) {
-	LOG_DISK("VerifyError (from write): %1 %2", e.message(), e.number());
+	LOG_DISK("VerifyError (from write): {} {}", e.message(), e.number());
 	if (nanomsg) {
 		DiskWriterBackEndResponse::error(e.message(), e.number(), 0).write_to_nanomsg(*nanomsg, LONG_TIMEOUT);
 	}
 } catch (exception& e) {
-	LOG_DISK("Exception (from write): %1", e.what());
+	LOG_DISK("Exception (from write): {}", e.what());
 	if (nanomsg) {
 		DiskWriterBackEndResponse::error(e.what(), 0, 0).write_to_nanomsg(*nanomsg, LONG_TIMEOUT);
 	}
diff --git a/src/lib/ffmpeg.cc b/src/lib/ffmpeg.cc
index c6867c081..f9a5dc9b6 100644
--- a/src/lib/ffmpeg.cc
+++ b/src/lib/ffmpeg.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "dcpomatic_log.h"
 #include "digester.h"
@@ -37,6 +36,7 @@ extern "C" {
 #include <libavformat/avformat.h>
 #include <libswscale/swscale.h>
 }
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <iostream>
 
@@ -218,7 +218,7 @@ FFmpeg::setup_decoders ()
 				throw DecodeError (N_("avcodec_open2"), N_("FFmpeg::setup_decoders"), r);
 			}
 		} else {
-			dcpomatic_log->log (String::compose ("No codec found for stream %1", i), LogEntry::TYPE_WARNING);
+			dcpomatic_log->log(fmt::format("No codec found for stream {}", i), LogEntry::TYPE_WARNING);
 		}
 	}
 }
diff --git a/src/lib/ffmpeg_content.cc b/src/lib/ffmpeg_content.cc
index 49e4933a6..d28b7c073 100644
--- a/src/lib/ffmpeg_content.cc
+++ b/src/lib/ffmpeg_content.cc
@@ -20,7 +20,6 @@
 */
 
 #include "audio_content.h"
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "exceptions.h"
@@ -118,7 +117,7 @@ FFmpegContent::FFmpegContent(cxml::ConstNodePtr node, boost::optional<boost::fil
 		if (auto filter = Filter::from_id(i->content())) {
 			_filters.push_back(*filter);
 		} else {
-			notes.push_back(String::compose(_("%1 no longer supports the `%2' filter, so it has been turned off."), variant::dcpomatic(), i->content()));
+			notes.push_back(fmt::format(_("{} no longer supports the `{}' filter, so it has been turned off."), variant::dcpomatic(), i->content()));
 		}
 	}
 
@@ -346,11 +345,11 @@ string
 FFmpegContent::summary () const
 {
 	if (video && audio) {
-		return String::compose (_("%1 [movie]"), path_summary());
+		return fmt::format(_("{} [movie]"), path_summary());
 	} else if (video) {
-		return String::compose (_("%1 [video]"), path_summary());
+		return fmt::format(_("{} [video]"), path_summary());
 	} else if (audio) {
-		return String::compose (_("%1 [audio]"), path_summary());
+		return fmt::format(_("{} [audio]"), path_summary());
 	}
 
 	return path_summary ();
@@ -386,8 +385,8 @@ FFmpegContent::technical_summary () const
 		s += " - " + audio->technical_summary ();
 	}
 
-	return s + String::compose (
-		"ffmpeg: audio %1 subtitle %2 filters %3", as, ss, filt
+	return s + fmt::format(
+		"ffmpeg: audio {} subtitle {} filters {}", as, ss, filt
 		);
 }
 
@@ -560,14 +559,14 @@ FFmpegContent::add_properties (shared_ptr<const Film> film, list<UserProperty>&
 				/// file is limited, so that not all possible values are valid.
 				p.push_back (
 					UserProperty (
-						UserProperty::VIDEO, _("Colour range"), String::compose(_("Limited / video (%1-%2)"), lim_start, lim_end)
+						UserProperty::VIDEO, _("Colour range"), fmt::format(_("Limited / video ({}-{})"), lim_start, lim_end)
 						)
 					);
 				break;
 			case AVCOL_RANGE_JPEG:
 				/// TRANSLATORS: this means that the range of pixel values used in this
 				/// file is full, so that all possible pixel values are valid.
-				p.push_back(UserProperty(UserProperty::VIDEO, _("Colour range"), String::compose(_("Full (0-%1)"), total - 1)));
+				p.push_back(UserProperty(UserProperty::VIDEO, _("Colour range"), fmt::format(_("Full (0-{})"), total - 1)));
 				break;
 			default:
 				DCPOMATIC_ASSERT (false);
diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index 81ca14f7f..65bc148fa 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -27,7 +27,6 @@
 #include "audio_buffers.h"
 #include "audio_content.h"
 #include "audio_decoder.h"
-#include "compose.hpp"
 #include "dcpomatic_log.h"
 #include "exceptions.h"
 #include "ffmpeg_audio_stream.h"
@@ -109,7 +108,7 @@ FFmpegDecoder::FFmpegDecoder (shared_ptr<const Film> film, shared_ptr<const FFmp
 FFmpegDecoder::FlushResult
 FFmpegDecoder::flush ()
 {
-	LOG_DEBUG_PLAYER("Flush FFmpeg decoder: current state %1", static_cast<int>(_flush_state));
+	LOG_DEBUG_PLAYER("Flush FFmpeg decoder: current state {}", static_cast<int>(_flush_state));
 
 	switch (_flush_state) {
 	case FlushState::CODECS:
@@ -193,7 +192,7 @@ FFmpegDecoder::flush_fill()
 			   here.  I'm not sure if that's the right idea.
 			*/
 			if (a > ContentTime() && a < full_length) {
-				LOG_DEBUG_PLAYER("Flush inserts silence at %1", to_string(a));
+				LOG_DEBUG_PLAYER("Flush inserts silence at {}", to_string(a));
 				auto to_do = min (full_length - a, ContentTime::from_seconds (0.1));
 				auto silence = make_shared<AudioBuffers>(i->channels(), to_do.frames_ceil (i->frame_rate()));
 				silence->make_silent ();
@@ -220,12 +219,12 @@ FFmpegDecoder::pass ()
 	   Hence it makes sense to continue here in that case.
 	*/
 	if (r < 0 && r != AVERROR_INVALIDDATA) {
-		LOG_DEBUG_PLAYER("FFpmegDecoder::pass flushes because av_read_frame returned %1", r);
+		LOG_DEBUG_PLAYER("FFpmegDecoder::pass flushes because av_read_frame returned {}", r);
 		if (r != AVERROR_EOF) {
 			/* Maybe we should fail here, but for now we'll just finish off instead */
 			char buf[256];
 			av_strerror (r, buf, sizeof(buf));
-			LOG_ERROR (N_("error on av_read_frame (%1) (%2)"), &buf[0], r);
+			LOG_ERROR(N_("error on av_read_frame ({}) ({})"), &buf[0], r);
 		}
 
 		av_packet_free (&packet);
@@ -375,7 +374,7 @@ deinterleave_audio(AVFrame* frame)
 	break;
 
 	default:
-		throw DecodeError (String::compose(_("Unrecognised audio sample format (%1)"), static_cast<int>(format)));
+		throw DecodeError(fmt::format(_("Unrecognised audio sample format ({})"), static_cast<int>(format)));
 	}
 
 	return audio;
@@ -505,7 +504,7 @@ FFmpegDecoder::process_audio_frame (shared_ptr<FFmpegAudioStream> stream)
 			av_q2d(time_base))
 			+ _pts_offset;
 		LOG_DEBUG_PLAYER(
-			"Process audio with timestamp %1 (BET %2, timebase %3/%4, (PTS offset %5)",
+			"Process audio with timestamp {} (BET {}, timebase {}/{}, (PTS offset {})",
 			to_string(ct),
 			frame->best_effort_timestamp,
 			time_base.num,
@@ -526,7 +525,7 @@ FFmpegDecoder::process_audio_frame (shared_ptr<FFmpegAudioStream> stream)
 
 	if (ct < ContentTime()) {
 		LOG_WARNING (
-			"Crazy timestamp %1 for %2 samples in stream %3 (ts=%4 tb=%5, off=%6)",
+			"Crazy timestamp {} for {} samples in stream {} (ts={} tb={}, off={})",
 			to_string(ct),
 			data->frames(),
 			stream->id(),
@@ -554,10 +553,10 @@ FFmpegDecoder::decode_and_process_audio_packet (AVPacket* packet)
 	auto context = _codec_context[stream->index(_format_context)];
 	auto frame = audio_frame (stream);
 
-	LOG_DEBUG_PLAYER("Send audio packet on stream %1", stream->index(_format_context));
+	LOG_DEBUG_PLAYER("Send audio packet on stream {}", stream->index(_format_context));
 	int r = avcodec_send_packet (context, packet);
 	if (r < 0) {
-		LOG_WARNING("avcodec_send_packet returned %1 for an audio packet", r);
+		LOG_WARNING("avcodec_send_packet returned {} for an audio packet", r);
 	}
 	while (r >= 0) {
 		r = avcodec_receive_frame (context, frame);
@@ -587,7 +586,7 @@ FFmpegDecoder::decode_and_process_video_packet (AVPacket* packet)
 	do {
 		int r = avcodec_send_packet (context, packet);
 		if (r < 0) {
-			LOG_WARNING("avcodec_send_packet returned %1 for a video packet", r);
+			LOG_WARNING("avcodec_send_packet returned {} for a video packet", r);
 		}
 
 		/* EAGAIN means we should call avcodec_receive_frame and then re-send the same packet */
diff --git a/src/lib/ffmpeg_examiner.cc b/src/lib/ffmpeg_examiner.cc
index ca85ae3c5..de41e0390 100644
--- a/src/lib/ffmpeg_examiner.cc
+++ b/src/lib/ffmpeg_examiner.cc
@@ -196,7 +196,7 @@ FFmpegExaminer::FFmpegExaminer (shared_ptr<const FFmpegContent> c, shared_ptr<Jo
 		}
 	}
 
-	LOG_GENERAL("Temporal reference was %1", temporal_reference);
+	LOG_GENERAL("Temporal reference was {}", temporal_reference);
 	if (temporal_reference.find("T2T3B2B3T2T3B2B3") != string::npos || temporal_reference.find("B2B3T2T3B2B3T2T3") != string::npos) {
 		/* The magical sequence (taken from mediainfo) suggests that 2:3 pull-down is in use */
 		_pulldown = true;
@@ -223,7 +223,7 @@ FFmpegExaminer::video_packet (AVCodecContext* context, string& temporal_referenc
 	do {
 		int r = avcodec_send_packet (context, packet);
 		if (r < 0) {
-			LOG_WARNING("avcodec_send_packet returned %1 for a video packet", r);
+			LOG_WARNING("avcodec_send_packet returned {} for a video packet", r);
 		}
 
 		/* EAGAIN means we should call avcodec_receive_frame and then re-send the same packet */
@@ -266,7 +266,7 @@ FFmpegExaminer::audio_packet (AVCodecContext* context, shared_ptr<FFmpegAudioStr
 
 	int r = avcodec_send_packet (context, packet);
 	if (r < 0) {
-		LOG_WARNING("avcodec_send_packet returned %1 for an audio packet", r);
+		LOG_WARNING("avcodec_send_packet returned {} for an audio packet", r);
 		return false;
 	}
 
diff --git a/src/lib/ffmpeg_file_encoder.cc b/src/lib/ffmpeg_file_encoder.cc
index 7f74ae4f6..3314d5d82 100644
--- a/src/lib/ffmpeg_file_encoder.cc
+++ b/src/lib/ffmpeg_file_encoder.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "cross.h"
 #include "ffmpeg_file_encoder.h"
 #include "ffmpeg_wrapper.h"
@@ -32,6 +31,7 @@
 extern "C" {
 #include <libavutil/channel_layout.h>
 }
+#include <fmt/format.h>
 #include <iostream>
 
 #include "i18n.h"
@@ -61,7 +61,7 @@ public:
 	{
 		_codec = avcodec_find_encoder_by_name (codec_name.c_str());
 		if (!_codec) {
-			throw EncodeError (String::compose("avcodec_find_encoder_by_name failed for %1", codec_name));
+			throw EncodeError(fmt::format("avcodec_find_encoder_by_name failed for {}", codec_name));
 		}
 
 		_codec_context = avcodec_alloc_context3 (_codec);
@@ -268,7 +268,7 @@ FFmpegFileEncoder::FFmpegFileEncoder (
 
 	r = avio_open_boost (&_format_context->pb, _output, AVIO_FLAG_WRITE);
 	if (r < 0) {
-		throw EncodeError (String::compose(_("Could not open output file %1 (%2)"), _output.string(), r));
+		throw EncodeError(fmt::format(_("Could not open output file {} ({})"), _output.string(), r));
 	}
 
 	AVDictionary* options = nullptr;
@@ -316,7 +316,7 @@ FFmpegFileEncoder::setup_video ()
 {
 	_video_codec = avcodec_find_encoder_by_name (_video_codec_name.c_str());
 	if (!_video_codec) {
-		throw EncodeError (String::compose("avcodec_find_encoder_by_name failed for %1", _video_codec_name));
+		throw EncodeError(fmt::format("avcodec_find_encoder_by_name failed for {}", _video_codec_name));
 	}
 
 	_video_codec_context = avcodec_alloc_context3 (_video_codec);
diff --git a/src/lib/ffmpeg_film_encoder.cc b/src/lib/ffmpeg_film_encoder.cc
index a2d26fd66..ed47d5b4d 100644
--- a/src/lib/ffmpeg_film_encoder.cc
+++ b/src/lib/ffmpeg_film_encoder.cc
@@ -28,7 +28,7 @@
 #include "log.h"
 #include "player.h"
 #include "player_video.h"
-#include "compose.hpp"
+#include <fmt/format.h>
 #include <iostream>
 
 #include "i18n.h"
@@ -147,9 +147,9 @@ FFmpegFilmEncoder::go()
 		filename = dcp::filesystem::change_extension(filename, "");
 
 		if (files > 1) {
-			/// TRANSLATORS: _reel%1 here is to be added to an export filename to indicate
-			/// which reel it is.  Preserve the %1; it will be replaced with the reel number.
-			filename = filename.string() + String::compose(_("_reel%1"), i + 1);
+			/// TRANSLATORS: _reel{} here is to be added to an export filename to indicate
+			/// which reel it is.  Preserve the {}; it will be replaced with the reel number.
+			filename = filename.string() + fmt::format(_("_reel{}"), i + 1);
 		}
 
 		file_encoders.push_back (
@@ -198,7 +198,7 @@ FFmpegFilmEncoder::go()
 				}
 			} else {
 				if (e.code != Butler::Error::Code::FINISHED) {
-					throw DecodeError(String::compose("Error during decoding: %1", e.summary()));
+					throw DecodeError(fmt::format("Error during decoding: {}", e.summary()));
 				}
 			}
 		}
@@ -263,17 +263,17 @@ FFmpegFilmEncoder::FileEncoderSet::FileEncoderSet(
 		_encoders[Eyes::LEFT] = make_shared<FFmpegFileEncoder>(
 			video_frame_size, video_frame_rate, audio_frame_rate, channels, format,
 			// TRANSLATORS: L here is an abbreviation for "left", to indicate the left-eye part of a 3D export
-			audio_stream_per_channel, x264_crf, String::compose("%1_%2%3", output.string(), _("L"), extension)
+			audio_stream_per_channel, x264_crf, fmt::format("{}_{}{}", output.string(), _("L"), extension)
 			);
 		_encoders[Eyes::RIGHT] = make_shared<FFmpegFileEncoder>(
 			video_frame_size, video_frame_rate, audio_frame_rate, channels, format,
 			// TRANSLATORS: R here is an abbreviation for "right", to indicate the right-eye part of a 3D export
-			audio_stream_per_channel, x264_crf, String::compose("%1_%2%3", output.string(), _("R"), extension)
+			audio_stream_per_channel, x264_crf, fmt::format("{}_{}{}", output.string(), _("R"), extension)
 			);
 	} else {
 		_encoders[Eyes::BOTH] = make_shared<FFmpegFileEncoder>(
 			video_frame_size, video_frame_rate, audio_frame_rate, channels, format,
-			audio_stream_per_channel, x264_crf, String::compose("%1%2", output.string(), extension)
+			audio_stream_per_channel, x264_crf, fmt::format("{}{}", output.string(), extension)
 			);
 	}
 }
diff --git a/src/lib/ffmpeg_image_proxy.cc b/src/lib/ffmpeg_image_proxy.cc
index c9fcd0413..9ba8f8bf5 100644
--- a/src/lib/ffmpeg_image_proxy.cc
+++ b/src/lib/ffmpeg_image_proxy.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "cross.h"
 #include "dcpomatic_assert.h"
 #include "dcpomatic_socket.h"
@@ -161,7 +160,7 @@ FFmpegImageProxy::image (Image::Alignment alignment, optional<dcp::Size>) const
 		if (_path) {
 			throw OpenFileError (_path->string(), e, OpenFileError::READ);
 		} else {
-			boost::throw_exception(DecodeError(String::compose(_("Could not decode image (%1)"), e)));
+			boost::throw_exception(DecodeError(fmt::format(_("Could not decode image ({})"), e)));
 		}
 	}
 
diff --git a/src/lib/file_group.cc b/src/lib/file_group.cc
index 56a5c2c59..84893b790 100644
--- a/src/lib/file_group.cc
+++ b/src/lib/file_group.cc
@@ -24,13 +24,13 @@
  */
 
 
-#include "compose.hpp"
 #include "cross.h"
 #include "dcpomatic_assert.h"
 #include "exceptions.h"
 #include "file_group.h"
 #include <dcp/filesystem.h>
 #include <sndfile.h>
+#include <fmt/format.h>
 #include <cstdio>
 
 
@@ -169,7 +169,7 @@ FileGroup::read (uint8_t* buffer, int amount) const
 		}
 
 		if (_current_file->error()) {
-			throw FileError (String::compose("fread error %1", errno), _paths[_current_path]);
+			throw FileError(fmt::format("fread error {}", errno), _paths[_current_path]);
 		}
 
 		if (eof) {
diff --git a/src/lib/film.cc b/src/lib/film.cc
index a1babd317..3254ac105 100644
--- a/src/lib/film.cc
+++ b/src/lib/film.cc
@@ -30,7 +30,6 @@
 #include "audio_processor.h"
 #include "change_signaller.h"
 #include "cinema.h"
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "cross.h"
@@ -502,7 +501,7 @@ Film::write_metadata ()
 	try {
 		metadata()->write_to_file_formatted(filename.string());
 	} catch (xmlpp::exception& e) {
-		throw FileError(String::compose("Could not write metadata file (%1)", e.what()), filename);
+		throw FileError(fmt::format("Could not write metadata file ({})", e.what()), filename);
 	}
 	set_dirty (false);
 }
@@ -526,7 +525,7 @@ Film::read_metadata (optional<boost::filesystem::path> path)
 		if (dcp::filesystem::exists(file("metadata")) && !dcp::filesystem::exists(file(metadata_file))) {
 			throw runtime_error(
 				variant::insert_dcpomatic(
-					_("This film was created with an older version of %1, and unfortunately it cannot "
+					_("This film was created with an older version of {}, and unfortunately it cannot "
 					  "be loaded into this version.  You will need to create a new Film, re-add your "
 					  "content and set it up again.  Sorry!")
 					)
@@ -545,10 +544,10 @@ Film::read_metadata (optional<boost::filesystem::path> path)
 
 	_state_version = f.number_child<int> ("Version");
 	if (_state_version > current_state_version) {
-		throw runtime_error(variant::insert_dcpomatic(_("This film was created with a newer version of %1, and it cannot be loaded into this version.  Sorry!")));
+		throw runtime_error(variant::insert_dcpomatic(_("This film was created with a newer version of {}, and it cannot be loaded into this version.  Sorry!")));
 	} else if (_state_version < current_state_version) {
 		/* This is an older version; save a copy (if we haven't already) */
-		auto const older = path->parent_path() / String::compose("metadata.%1.xml", _state_version);
+		auto const older = path->parent_path() / fmt::format("metadata.{}.xml", _state_version);
 		if (!dcp::filesystem::is_regular_file(older)) {
 			try {
 				dcp::filesystem::copy_file(*path, older);
@@ -933,7 +932,7 @@ Film::isdcf_name (bool if_created_now) const
 				}
 			}
 		} else {
-			version = dcp::fmt::to_string(_version_number);
+			version = fmt::to_string(_version_number);
 		}
 		isdcf_name += "-" + version;
 	}
@@ -966,7 +965,7 @@ Film::isdcf_name (bool if_created_now) const
 		auto fl = _luminance->value_in_foot_lamberts();
 		char buffer[64];
 		snprintf (buffer, sizeof(buffer), "%.1f", fl);
-		isdcf_name += String::compose("-%1fl", buffer);
+		isdcf_name += fmt::format("-{}fl", buffer);
 	}
 
 	if (video_frame_rate() != 24) {
@@ -989,7 +988,7 @@ Film::isdcf_name (bool if_created_now) const
 				auto first_ratio = lrintf(scaled_size->ratio() * 100);
 				auto container_ratio = lrintf(container()->ratio() * 100);
 				if (first_ratio != container_ratio) {
-					isdcf_name += "-" + dcp::fmt::to_string(first_ratio);
+					isdcf_name += "-" + fmt::to_string(first_ratio);
 				}
 			}
 		}
@@ -1052,7 +1051,7 @@ Film::isdcf_name (bool if_created_now) const
 	if (!ch.first && !ch.second) {
 		isdcf_name += "_MOS";
 	} else if (ch.first) {
-		isdcf_name += String::compose("_%1%2", ch.first, ch.second);
+		isdcf_name += fmt::format("_{}{}", ch.first, ch.second);
 	}
 
 	if (audio_channels() > static_cast<int>(dcp::Channel::HI) && find(mapped.begin(), mapped.end(), static_cast<int>(dcp::Channel::HI)) != mapped.end()) {
@@ -1650,7 +1649,7 @@ Film::check_reel_boundaries_for_atmos()
 		} else {
 			set_reel_type(ReelType::SINGLE);
 		}
-		Message(variant::insert_dcpomatic("%1 had to change your reel settings to accomodate the Atmos content"));
+		Message(variant::insert_dcpomatic("{} had to change your reel settings to accomodate the Atmos content"));
 	}
 }
 
@@ -1672,7 +1671,7 @@ Film::check_settings_consistency ()
 		Message(_("You have more than one piece of Atmos content, and they do not have the same frame rate.  You must remove some Atmos content."));
 	} else if (atmos_rates.size() == 1 && *atmos_rates.begin() != video_frame_rate()) {
 		set_video_frame_rate(*atmos_rates.begin(), false);
-		Message(variant::insert_dcpomatic(_("%1 had to change your settings so that the film's frame rate is the same as that of your Atmos content.")));
+		Message(variant::insert_dcpomatic(_("{} had to change your settings so that the film's frame rate is the same as that of your Atmos content.")));
 	}
 
 	if (!atmos_rates.empty()) {
@@ -1706,7 +1705,7 @@ Film::check_settings_consistency ()
 	}
 
 	if (change_made) {
-		Message(variant::insert_dcpomatic(_("%1 had to change your settings for referring to DCPs as OV.  Please review those settings to make sure they are what you want.")));
+		Message(variant::insert_dcpomatic(_("{} had to change your settings for referring to DCPs as OV.  Please review those settings to make sure they are what you want.")));
 	}
 
 	if (reel_type() == ReelType::CUSTOM) {
@@ -1717,9 +1716,9 @@ Film::check_settings_consistency ()
 
 		if (too_late != boundaries.end()) {
 			if (std::distance(too_late, boundaries.end()) > 1) {
-				Message(variant::insert_dcpomatic(_("%1 had to remove some of your custom reel boundaries as they no longer lie within the film.")));
+				Message(variant::insert_dcpomatic(_("{} had to remove some of your custom reel boundaries as they no longer lie within the film.")));
 			} else {
-				Message(variant::insert_dcpomatic(_("%1 had to remove one of your custom reel boundaries as it no longer lies within the film.")));
+				Message(variant::insert_dcpomatic(_("{} had to remove one of your custom reel boundaries as it no longer lies within the film.")));
 			}
 			boundaries.erase(too_late, boundaries.end());
 			set_custom_reel_boundaries(boundaries);
@@ -1842,7 +1841,7 @@ Film::make_kdm(boost::filesystem::path cpl_file, dcp::LocalTime from, dcp::Local
 		bool done = false;
 		for (auto const& k: imported_keys) {
 			if (k.id() == asset->key_id().get()) {
-				LOG_GENERAL("Using imported key for %1", asset->key_id().get());
+				LOG_GENERAL("Using imported key for {}", asset->key_id().get());
 				keys[asset] = k.key();
 				done = true;
 			}
@@ -1850,7 +1849,7 @@ Film::make_kdm(boost::filesystem::path cpl_file, dcp::LocalTime from, dcp::Local
 
 		if (!done) {
 			/* No imported key; it must be an asset that we encrypted */
-			LOG_GENERAL("Using our own key for %1", asset->key_id().get());
+			LOG_GENERAL("Using our own key for {}", asset->key_id().get());
 			keys[asset] = key();
 		}
 	}
@@ -2454,9 +2453,9 @@ Film::read_remembered_assets() const
 			assets.push_back(RememberedAsset(node));
 		}
 	} catch (std::exception& e) {
-		LOG_ERROR("Could not read assets file %1 (%2)", filename, e.what());
+		LOG_ERROR("Could not read assets file {} ({})", filename.string(), e.what());
 	} catch (...) {
-		LOG_ERROR("Could not read assets file %1", filename);
+		LOG_ERROR("Could not read assets file {}", filename.string());
 	}
 
 	return assets;
@@ -2476,8 +2475,8 @@ Film::write_remembered_assets(vector<RememberedAsset> const& assets) const
 	try {
 		doc->write_to_file_formatted(dcp::filesystem::fix_long_path(file(assets_file)).string());
 	} catch (std::exception& e) {
-		LOG_ERROR("Could not write assets file %1 (%2)", file(assets_file), e.what());
+		LOG_ERROR("Could not write assets file {} ({})", file(assets_file).string(), e.what());
 	} catch (...) {
-		LOG_ERROR("Could not write assets file %1", file(assets_file));
+		LOG_ERROR("Could not write assets file {}", file(assets_file).string());
 	}
 }
diff --git a/src/lib/filter_graph.cc b/src/lib/filter_graph.cc
index 745d980a4..178c93a25 100644
--- a/src/lib/filter_graph.cc
+++ b/src/lib/filter_graph.cc
@@ -28,12 +28,12 @@
 #include "filter.h"
 #include "exceptions.h"
 #include "image.h"
-#include "compose.hpp"
 extern "C" {
 #include <libavfilter/buffersrc.h>
 #include <libavfilter/buffersink.h>
 #include <libavformat/avio.h>
 }
+#include <fmt/format.h>
 #include <iostream>
 
 #include "i18n.h"
@@ -105,7 +105,7 @@ FilterGraph::setup(vector<Filter> const& filters)
 
 	int e = avfilter_graph_config (_graph, 0);
 	if (e < 0) {
-		throw DecodeError (String::compose(N_("could not configure filter graph (%1)"), e));
+		throw DecodeError(fmt::format(N_("could not configure filter graph ({})"), e));
 	}
 }
 
diff --git a/src/lib/font_config.cc b/src/lib/font_config.cc
index 653c9ba84..410f27541 100644
--- a/src/lib/font_config.cc
+++ b/src/lib/font_config.cc
@@ -125,18 +125,18 @@ FontConfig::system_font_with_name(string name)
 {
 	optional<boost::filesystem::path> path;
 
-	LOG_GENERAL("Searching system for font %1", name);
+	LOG_GENERAL("Searching system for font {}", name);
 	auto pattern = FcNameParse(reinterpret_cast<FcChar8 const*>(name.c_str()));
 	auto object_set = FcObjectSetBuild(FC_FILE, nullptr);
 	auto font_set = FcFontList(_config, pattern, object_set);
 	if (font_set) {
-		LOG_GENERAL("%1 candidate fonts found", font_set->nfont);
+		LOG_GENERAL("{} candidate fonts found", font_set->nfont);
 		for (int i = 0; i < font_set->nfont; ++i) {
 			auto font = font_set->fonts[i];
 			FcChar8* file;
 			if (FcPatternGetString(font, FC_FILE, 0, &file) == FcResultMatch) {
 				path = boost::filesystem::path(reinterpret_cast<char*>(file));
-				LOG_GENERAL("Found %1", *path);
+				LOG_GENERAL("Found {}", path->string());
 				break;
 			}
 		}
@@ -149,9 +149,9 @@ FontConfig::system_font_with_name(string name)
 	FcPatternDestroy(pattern);
 
 	if (path) {
-		LOG_GENERAL("Searched system for font %1, found %2", name, *path);
+		LOG_GENERAL("Searched system for font {}, found {}", name, path->string());
 	} else {
-		LOG_GENERAL("Searched system for font %1; nothing found", name);
+		LOG_GENERAL("Searched system for font {}; nothing found", name);
 	}
 
 	return path;
diff --git a/src/lib/font_id_allocator.cc b/src/lib/font_id_allocator.cc
index b85fc90dc..59db72a09 100644
--- a/src/lib/font_id_allocator.cc
+++ b/src/lib/font_id_allocator.cc
@@ -19,13 +19,13 @@
 */
 
 
-#include "compose.hpp"
 #include "constants.h"
 #include "dcpomatic_assert.h"
 #include "font_id_allocator.h"
 #include <dcp/reel.h>
 #include <dcp/reel_text_asset.h>
 #include <dcp/text_asset.h>
+#include <fmt/format.h>
 #include <set>
 #include <string>
 #include <vector>
@@ -88,7 +88,7 @@ FontIDAllocator::allocate()
 		auto proposed = font.first.font_id;
 		int prefix = 0;
 		while (used_ids.find(proposed) != used_ids.end()) {
-			proposed = String::compose("%1_%2", prefix++, font.first.font_id);
+			proposed = fmt::format("{}_{}", prefix++, font.first.font_id);
 			DCPOMATIC_ASSERT(prefix < 128);
 		}
 		font.second = proposed;
diff --git a/src/lib/frame_rate_change.cc b/src/lib/frame_rate_change.cc
index 8372493ef..a531ad319 100644
--- a/src/lib/frame_rate_change.cc
+++ b/src/lib/frame_rate_change.cc
@@ -19,10 +19,10 @@
 */
 
 
-#include "compose.hpp"
 #include "content.h"
 #include "film.h"
 #include "frame_rate_change.h"
+#include <fmt/format.h>
 #include <cmath>
 
 #include "i18n.h"
@@ -93,7 +93,7 @@ FrameRateChange::description () const
 		} else if (repeat == 2) {
 			description = _("Each content frame will be doubled in the DCP.\n");
 		} else if (repeat > 2) {
-			description = String::compose (_("Each content frame will be repeated %1 more times in the DCP.\n"), repeat - 1);
+			description = fmt::format(_("Each content frame will be repeated {} more times in the DCP.\n"), repeat - 1);
 		}
 
 		if (change_speed) {
diff --git a/src/lib/grok_j2k_encoder_thread.cc b/src/lib/grok_j2k_encoder_thread.cc
index e6c256f11..f7476f920 100644
--- a/src/lib/grok_j2k_encoder_thread.cc
+++ b/src/lib/grok_j2k_encoder_thread.cc
@@ -51,16 +51,16 @@ try
 {
 	while (true)
 	{
-		LOG_TIMING("encoder-sleep thread=%1", thread_id());
+		LOG_TIMING("encoder-sleep thread={}", thread_id());
 		auto frame = _encoder.pop();
 
 		dcp::ScopeGuard frame_guard([this, &frame]() {
-			LOG_ERROR("Failed to schedule encode of %1 using grok", frame.index());
+			LOG_ERROR("Failed to schedule encode of {} using grok", frame.index());
 			_errors++;
 			_encoder.retry(frame);
 		});
 
-		LOG_TIMING("encoder-pop thread=%1 frame=%2 eyes=%3", thread_id(), frame.index(), static_cast<int>(frame.eyes()));
+		LOG_TIMING("encoder-pop thread={} frame={} eyes={}", thread_id(), frame.index(), static_cast<int>(frame.eyes()));
 
 		auto grok = Config::instance()->grok().get_value_or({});
 
diff --git a/src/lib/hints.cc b/src/lib/hints.cc
index b929a3746..14fb5f023 100644
--- a/src/lib/hints.cc
+++ b/src/lib/hints.cc
@@ -22,7 +22,6 @@
 #include "audio_analysis.h"
 #include "audio_content.h"
 #include "audio_processor.h"
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "content.h"
@@ -110,7 +109,7 @@ Hints::check_few_audio_channels ()
 			variant::insert_dcpomatic(
 				_("Your DCP has fewer than 6 audio channels.  This may cause problems on some projectors.  "
 				  "You may want to set the DCP to have 6 channels.  It does not matter if your content has "
-				  "fewer channels, as %1 will fill the extras with silence.")
+				  "fewer channels, as {} will fill the extras with silence.")
 				)
 		    );
 	}
@@ -123,7 +122,7 @@ Hints::check_upmixers ()
 	auto ap = film()->audio_processor();
 	if (ap && (ap->id() == "stereo-5.1-upmix-a" || ap->id() == "stereo-5.1-upmix-b")) {
 		hint(variant::insert_dcpomatic(
-				_("You are using %1's stereo-to-5.1 upmixer.  This is experimental and "
+				_("You are using {}'s stereo-to-5.1 upmixer.  This is experimental and "
 				  "may result in poor-quality audio.  If you continue, you should listen to the "
 				  "resulting DCP in a cinema to make sure that it sounds good.")
 				)
@@ -190,7 +189,7 @@ Hints::check_frame_rate ()
 	case 25:
 	{
 		/* You might want to go to 24 */
-		string base = String::compose(_("You are set up for a DCP at a frame rate of %1 fps.  This frame rate is not supported by all projectors.  You may want to consider changing your frame rate to %2 fps."), 25, 24);
+		string base = fmt::format(_("You are set up for a DCP at a frame rate of {} fps.  This frame rate is not supported by all projectors.  You may want to consider changing your frame rate to {} fps."), 25, 24);
 		if (f->interop()) {
 			base += "  ";
 			base += _("If you do use 25fps you should change your DCP standard to SMPTE.");
@@ -206,7 +205,7 @@ Hints::check_frame_rate ()
 	case 50:
 	case 60:
 		/* You almost certainly want to go to half frame rate */
-		hint (String::compose(_("You are set up for a DCP at a frame rate of %1 fps.  This frame rate is not supported by all projectors.  It is advisable to change the DCP frame rate to %2 fps."), f->video_frame_rate(), f->video_frame_rate() / 2));
+		hint (fmt::format(_("You are set up for a DCP at a frame rate of {} fps.  This frame rate is not supported by all projectors.  It is advisable to change the DCP frame rate to {} fps."), f->video_frame_rate(), f->video_frame_rate() / 2));
 		break;
 	}
 }
@@ -304,7 +303,7 @@ Hints::check_vob ()
 	}
 
 	if (vob > 1) {
-		hint (String::compose (_("You have %1 files that look like they are VOB files from DVD. You should join them to ensure smooth joins between the files."), vob));
+		hint (fmt::format(_("You have {} files that look like they are VOB files from DVD. You should join them to ensure smooth joins between the files."), vob));
 	}
 }
 
@@ -353,8 +352,8 @@ Hints::check_loudness ()
 		ch = ch.substr (0, ch.length() - 2);
 
 		if (!ch.empty()) {
-			hint(String::compose(
-					_("Your audio level is very high (on %1).  You should reduce the gain of your audio content."),
+			hint(fmt::format(
+					_("Your audio level is very high (on {}).  You should reduce the gain of your audio content."),
 					ch
 					)
 			     );
@@ -589,9 +588,9 @@ Hints::closed_caption (PlayerText text, DCPTimePeriod period)
 			if (!_long_ccap) {
 				_long_ccap = true;
 				hint (
-					String::compose(
-						"At least one of your closed caption lines has more than %1 characters.  "
-						"It is advisable to make each line %1 characters at most in length.",
+					fmt::format(
+						"At least one of your closed caption lines has more than {} characters.  "
+						"It is advisable to make each line {} characters at most in length.",
 						MAX_CLOSED_CAPTION_LENGTH,
 						MAX_CLOSED_CAPTION_LENGTH)
 				     );
@@ -600,7 +599,7 @@ Hints::closed_caption (PlayerText text, DCPTimePeriod period)
 	}
 
 	if (!_too_many_ccap_lines && lines > MAX_CLOSED_CAPTION_LINES) {
-		hint (String::compose(_("Some of your closed captions span more than %1 lines, so they will be truncated."), MAX_CLOSED_CAPTION_LINES));
+		hint (fmt::format(_("Some of your closed captions span more than {} lines, so they will be truncated."), MAX_CLOSED_CAPTION_LINES));
 		_too_many_ccap_lines = true;
 	}
 
@@ -739,7 +738,7 @@ Hints::check_certificates ()
 	switch (*bad) {
 	case Config::BAD_SIGNER_UTF8_STRINGS:
 		hint(variant::insert_dcpomatic(
-				_("The certificate chain that %1 uses for signing DCPs and KDMs contains a small error "
+				_("The certificate chain that {} uses for signing DCPs and KDMs contains a small error "
 				  "which will prevent DCPs from being validated correctly on some systems.  It is advisable to "
 				  "re-create the signing certificate chain by clicking the \"Re-make certificates and key...\" "
 				  "button in the Keys page of Preferences.")
@@ -747,7 +746,7 @@ Hints::check_certificates ()
 		break;
 	case Config::BAD_SIGNER_VALIDITY_TOO_LONG:
 		hint(variant::insert_dcpomatic(
-				_("The certificate chain that %1 uses for signing DCPs and KDMs has a validity period "
+				_("The certificate chain that {} uses for signing DCPs and KDMs has a validity period "
 				  "that is too long.  This will cause problems playing back DCPs on some systems. "
 				  "It is advisable to re-create the signing certificate chain by clicking the "
 				  "\"Re-make certificates and key...\" button in the Keys page of Preferences.")
@@ -765,7 +764,7 @@ Hints::check_8_or_16_audio_channels()
 {
 	auto const channels = film()->audio_channels();
 	if (film()->video_encoding() != VideoEncoding::MPEG2 && channels != 8 && channels != 16) {
-		hint(String::compose(_("Your DCP has %1 audio channels, rather than 8 or 16.  This may cause some distributors to raise QC errors when they check your DCP.  To avoid this, set the DCP audio channels to 8 or 16."), channels));
+		hint(fmt::format(_("Your DCP has {} audio channels, rather than 8 or 16.  This may cause some distributors to raise QC errors when they check your DCP.  To avoid this, set the DCP audio channels to 8 or 16."), channels));
 	}
 }
 
diff --git a/src/lib/http_server.cc b/src/lib/http_server.cc
index 0ee62756a..90c54bcff 100644
--- a/src/lib/http_server.cc
+++ b/src/lib/http_server.cc
@@ -25,6 +25,7 @@
 #include "http_server.h"
 #include "util.h"
 #include "variant.h"
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <stdexcept>
 
@@ -72,7 +73,7 @@ Response::add_header(string key, string value)
 void
 Response::send(shared_ptr<Socket> socket)
 {
-	socket->write(String::compose("HTTP/1.1 %1 OK\r\n", _code));
+	socket->write(fmt::format("HTTP/1.1 {} OK\r\n", _code));
 	switch (_type) {
 	case Type::HTML:
 		socket->write("Content-Type: text/html; charset=utf-8\r\n");
@@ -81,9 +82,9 @@ Response::send(shared_ptr<Socket> socket)
 		socket->write("Content-Type: text/json; charset=utf-8\r\n");
 		break;
 	}
-	socket->write(String::compose("Content-Length: %1\r\n", _payload.length()));
+	socket->write(fmt::format("Content-Length: {}\r\n", _payload.length()));
 	for (auto const& header: _headers) {
-		socket->write(String::compose("%1: %2\r\n", header.first, header.second));
+		socket->write(fmt::format("{}: {}\r\n", header.first, header.second));
 	}
 	socket->write("\r\n");
 	socket->write(_payload);
@@ -94,21 +95,21 @@ Response
 HTTPServer::get(string const& url)
 {
 	if (url == "/") {
-		return Response(200, String::compose(dcp::file_to_string(resources_path() / "web" / "index.html"), variant::dcpomatic_player()));
+		return Response(200, fmt::format(dcp::file_to_string(resources_path() / "web" / "index.html"), variant::dcpomatic_player()));
 	} else if (url == "/api/v1/status") {
 		auto json = string{"{ "};
 		{
 			boost::mutex::scoped_lock lm(_mutex);
-			json += String::compose("\"playing\": %1, ", _playing ? "true" : "false");
-			json += String::compose("\"position\": \"%1\", ", seconds_to_hms(_position.seconds()));
-			json += String::compose("\"dcp_name\": \"%1\"", _dcp_name);
+			json += fmt::format("\"playing\": {}, ", _playing ? "true" : "false");
+			json += fmt::format("\"position\": \"{}\", ", seconds_to_hms(_position.seconds()));
+			json += fmt::format("\"dcp_name\": \"{}\"", _dcp_name);
 		}
 		json += " }";
 		auto response = Response(200, json);
 		response.set_type(Response::Type::JSON);
 		return response;
 	} else {
-		LOG_HTTP("404 %1", url);
+		LOG_HTTP("404 {}", url);
 		return Response::ERROR_404;
 	}
 }
@@ -144,19 +145,19 @@ HTTPServer::request(vector<string> const& request)
 
 	try {
 		if (parts[0] == "GET") {
-			LOG_HTTP("GET %1", parts[1]);
+			LOG_HTTP("GET {}", parts[1]);
 			return get(parts[1]);
 		} else if (parts[0] == "POST") {
-			LOG_HTTP("POST %1", parts[1]);
+			LOG_HTTP("POST {}", parts[1]);
 			return post(parts[1]);
 		}
 	} catch (std::exception& e) {
-		LOG_ERROR("Error while handling HTTP request: %1", e.what());
+		LOG_ERROR("Error while handling HTTP request: {}", e.what());
 	} catch (...) {
 		LOG_ERROR_NC("Unknown exception while handling HTTP request");
 	}
 
-	LOG_HTTP("404 %1", parts[0]);
+	LOG_HTTP("404 {}", parts[0]);
 	return Response::ERROR_404;
 }
 
@@ -191,7 +192,7 @@ HTTPServer::handle(shared_ptr<Socket> socket)
 					} else if (_line.size() >= 2) {
 						_line = _line.substr(0, _line.length() - 2);
 					}
-					LOG_HTTP("Receive: %1", _line);
+					LOG_HTTP("Receive: {}", _line);
 					_request.push_back(_line);
 					_line = "";
 				}
diff --git a/src/lib/image_examiner.cc b/src/lib/image_examiner.cc
index 15a0b043d..02afd6ab5 100644
--- a/src/lib/image_examiner.cc
+++ b/src/lib/image_examiner.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "cross.h"
 #include "exceptions.h"
@@ -33,6 +32,7 @@
 #include <dcp/exceptions.h>
 #include <dcp/filesystem.h>
 #include <dcp/j2k_transcode.h>
+#include <fmt/format.h>
 #include <iostream>
 
 #include "i18n.h"
@@ -62,7 +62,7 @@ ImageExaminer::ImageExaminer (shared_ptr<const Film> film, shared_ptr<const Imag
 		try {
 			_video_size = dcp::decompress_j2k(buffer.data(), size, 0)->size();
 		} catch (dcp::ReadError& e) {
-			throw DecodeError (String::compose (_("Could not decode JPEG2000 file %1 (%2)"), path, e.what ()));
+			throw DecodeError(fmt::format(_("Could not decode JPEG2000 file {} ({})"), path.string(), e.what()));
 		}
 	} else {
 		FFmpegImageProxy proxy(content->path(0));
diff --git a/src/lib/image_png.cc b/src/lib/image_png.cc
index b97ef5aad..0817a6944 100644
--- a/src/lib/image_png.cc
+++ b/src/lib/image_png.cc
@@ -23,6 +23,7 @@
 #include "exceptions.h"
 #include "image.h"
 #include <png.h>
+#include <fmt/format.h>
 
 #include "i18n.h"
 
@@ -78,7 +79,7 @@ png_flush (png_structp)
 static void
 png_error_fn (png_structp, char const * message)
 {
-	throw EncodeError (String::compose("Error during PNG write: %1", message));
+	throw EncodeError(fmt::format("Error during PNG write: {}", message));
 }
 
 
diff --git a/src/lib/internet.cc b/src/lib/internet.cc
index 8c5b99e61..b9ec753c7 100644
--- a/src/lib/internet.cc
+++ b/src/lib/internet.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "cross.h"
 #include "exceptions.h"
 #include "scoped_temporary.h"
@@ -121,7 +120,7 @@ get_from_url (string url, bool pasv, bool skip_pasv_ip, ScopedTemporary& temp)
 	f.close();
 	curl_easy_cleanup (curl);
 	if (cr != CURLE_OK) {
-		return String::compose (_("Download failed (%1 error %2)"), url, (int) cr);
+		return fmt::format(_("Download failed ({} error {})"), url, static_cast<int>(cr));
 	}
 
 	return {};
@@ -176,7 +175,7 @@ get_from_zip_url (string url, string file, bool pasv, bool skip_pasv_ip, functio
 	zip_error_init (&error);
 	auto zip = zip_open_from_source (zip_source, ZIP_RDONLY, &error);
 	if (!zip) {
-		return String::compose (_("Could not open downloaded ZIP file (%1:%2: %3)"), error.zip_err, error.sys_err, error.str ? error.str : "");
+		return fmt::format(_("Could not open downloaded ZIP file ({}:{}: {})"), error.zip_err, error.sys_err, error.str ? error.str : "");
 	}
 
 #else
diff --git a/src/lib/j2k_encoder.cc b/src/lib/j2k_encoder.cc
index 309fce0b3..4b48bc220 100644
--- a/src/lib/j2k_encoder.cc
+++ b/src/lib/j2k_encoder.cc
@@ -24,7 +24,6 @@
  */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "cross.h"
 #include "dcp_video.h"
@@ -198,7 +197,7 @@ J2KEncoder::end()
 {
 	boost::mutex::scoped_lock lock (_queue_mutex);
 
-	LOG_GENERAL (N_("Clearing queue of %1"), _queue.size ());
+	LOG_GENERAL(N_("Clearing queue of {}"), _queue.size ());
 
 	/* Keep waking workers until the queue is empty */
 	while (!_queue.empty ()) {
@@ -214,7 +213,7 @@ J2KEncoder::end()
 	/* Something might have been thrown during terminate_threads */
 	rethrow ();
 
-	LOG_GENERAL (N_("Mopping up %1"), _queue.size());
+	LOG_GENERAL(N_("Mopping up {}"), _queue.size());
 
 	/* The following sequence of events can occur in the above code:
 	     1. a remote worker takes the last image off the queue
@@ -228,14 +227,14 @@ J2KEncoder::end()
 #ifdef DCPOMATIC_GROK
 		if (Config::instance()->grok().get_value_or({}).enable) {
 			if (!_context->scheduleCompress(i)){
-				LOG_GENERAL (N_("[%1] J2KEncoder thread pushes frame %2 back onto queue after failure"), thread_id(), i.index());
+				LOG_GENERAL(N_("[{}] J2KEncoder thread pushes frame {} back onto queue after failure"), thread_id(), i.index());
 				// handle error
 			}
 		} else {
 #else
 		{
 #endif
-			LOG_GENERAL(N_("Encode left-over frame %1"), i.index());
+			LOG_GENERAL(N_("Encode left-over frame {}"), i.index());
 			try {
 				_writer.write(
 					make_shared<dcp::ArrayData>(i.encode_locally()),
@@ -244,7 +243,7 @@ J2KEncoder::end()
 					);
 				frame_done ();
 			} catch (std::exception& e) {
-				LOG_ERROR (N_("Local encode failed (%1)"), e.what ());
+				LOG_ERROR(N_("Local encode failed ({})"), e.what ());
 			}
 		}
 	}
@@ -297,9 +296,9 @@ J2KEncoder::encode (shared_ptr<PlayerVideo> pv, DCPTime time)
 	   when there are no threads.
 	*/
 	while (_queue.size() >= (threads * 2) + 1) {
-		LOG_TIMING ("decoder-sleep queue=%1 threads=%2", _queue.size(), threads);
+		LOG_TIMING("decoder-sleep queue={} threads={}", _queue.size(), threads);
 		_full_condition.wait (queue_lock);
-		LOG_TIMING ("decoder-wake queue=%1 threads=%2", _queue.size(), threads);
+		LOG_TIMING("decoder-wake queue={} threads={}", _queue.size(), threads);
 	}
 
 	_writer.rethrow();
@@ -313,21 +312,21 @@ J2KEncoder::encode (shared_ptr<PlayerVideo> pv, DCPTime time)
 
 	if (_writer.can_fake_write(position)) {
 		/* We can fake-write this frame */
-		LOG_DEBUG_ENCODE("Frame @ %1 FAKE", to_string(time));
+		LOG_DEBUG_ENCODE("Frame @ {} FAKE", to_string(time));
 		_writer.fake_write(position, pv->eyes ());
 		frame_done ();
 	} else if (pv->has_j2k() && !_film->reencode_j2k()) {
-		LOG_DEBUG_ENCODE("Frame @ %1 J2K", to_string(time));
+		LOG_DEBUG_ENCODE("Frame @ {} J2K", to_string(time));
 		/* This frame already has J2K data, so just write it */
 		_writer.write(pv->j2k(), position, pv->eyes ());
 		frame_done ();
 	} else if (_last_player_video[pv->eyes()] && _writer.can_repeat(position) && pv->same(_last_player_video[pv->eyes()])) {
-		LOG_DEBUG_ENCODE("Frame @ %1 REPEAT", to_string(time));
+		LOG_DEBUG_ENCODE("Frame @ {} REPEAT", to_string(time));
 		_writer.repeat(position, pv->eyes());
 	} else {
-		LOG_DEBUG_ENCODE("Frame @ %1 ENCODE", to_string(time));
+		LOG_DEBUG_ENCODE("Frame @ {} ENCODE", to_string(time));
 		/* Queue this new frame for encoding */
-		LOG_TIMING ("add-frame-to-queue queue=%1", _queue.size ());
+		LOG_TIMING("add-frame-to-queue queue={}", _queue.size ());
 		auto dcpv = DCPVideo(
 				pv,
 				position,
@@ -365,7 +364,7 @@ J2KEncoder::terminate_threads ()
 void
 J2KEncoder::remake_threads(int cpu, int gpu, list<EncodeServerDescription> servers)
 {
-	LOG_GENERAL("Making threads: CPU=%1, GPU=%2, Remote=%3", cpu, gpu, servers.size());
+	LOG_GENERAL("Making threads: CPU={}, GPU={}, Remote={}", cpu, gpu, servers.size());
 	if ((cpu + gpu + servers.size()) == 0) {
 		/* Make at least one thread, even if all else fails.  Maybe we are configured
 		 * for "only servers encode" but no servers have been registered yet.
@@ -440,9 +439,9 @@ J2KEncoder::remake_threads(int cpu, int gpu, list<EncodeServerDescription> serve
 		auto const wanted_threads = server.threads();
 
 		if (wanted_threads > current_threads) {
-			LOG_GENERAL(N_("Adding %1 worker threads for remote %2"), wanted_threads - current_threads, server.host_name());
+			LOG_GENERAL(N_("Adding {} worker threads for remote {}"), wanted_threads - current_threads, server.host_name());
 		} else if (wanted_threads < current_threads) {
-			LOG_GENERAL(N_("Removing %1 worker threads for remote %2"), current_threads - wanted_threads, server.host_name());
+			LOG_GENERAL(N_("Removing {} worker threads for remote {}"), current_threads - wanted_threads, server.host_name());
 		}
 
 		for (auto i = current_threads; i < wanted_threads; ++i) {
@@ -466,7 +465,7 @@ J2KEncoder::pop()
 		_empty_condition.wait (lock);
 	}
 
-	LOG_TIMING("encoder-wake thread=%1 queue=%2", thread_id(), _queue.size());
+	LOG_TIMING("encoder-wake thread={} queue={}", thread_id(), _queue.size());
 
 	auto vf = _queue.front();
 	_queue.pop_front();
diff --git a/src/lib/j2k_encoder_thread.cc b/src/lib/j2k_encoder_thread.cc
index d0e8a439c..b6f927ceb 100644
--- a/src/lib/j2k_encoder_thread.cc
+++ b/src/lib/j2k_encoder_thread.cc
@@ -49,7 +49,7 @@ J2KEncoderThread::stop()
 	try {
 		_thread.join();
 	} catch (std::exception& e) {
-		LOG_ERROR("join() threw an exception: %1", e.what());
+		LOG_ERROR("join() threw an exception: {}", e.what());
 	} catch (...) {
 		LOG_ERROR_NC("join() threw an exception");
 	}
diff --git a/src/lib/j2k_sync_encoder_thread.cc b/src/lib/j2k_sync_encoder_thread.cc
index ef6834f60..9df6c253a 100644
--- a/src/lib/j2k_sync_encoder_thread.cc
+++ b/src/lib/j2k_sync_encoder_thread.cc
@@ -40,7 +40,7 @@ try
 	log_thread_start();
 
 	while (true) {
-		LOG_TIMING("encoder-sleep thread=%1", thread_id());
+		LOG_TIMING("encoder-sleep thread={}", thread_id());
 		auto frame = _encoder.pop();
 
 		dcp::ScopeGuard frame_guard([this, &frame]() {
@@ -48,7 +48,7 @@ try
 			_encoder.retry(frame);
 		});
 
-		LOG_TIMING("encoder-pop thread=%1 frame=%2 eyes=%3", thread_id(), frame.index(), static_cast<int>(frame.eyes()));
+		LOG_TIMING("encoder-pop thread={} frame={} eyes={}", thread_id(), frame.index(), static_cast<int>(frame.eyes()));
 
 		auto encoded = encode(frame);
 
diff --git a/src/lib/job.cc b/src/lib/job.cc
index ee6ad4e70..8891f83c2 100644
--- a/src/lib/job.cc
+++ b/src/lib/job.cc
@@ -24,7 +24,6 @@
  */
 
 
-#include "compose.hpp"
 #include "constants.h"
 #include "cross.h"
 #include "dcpomatic_log.h"
@@ -105,7 +104,7 @@ Job::start ()
 void
 Job::run_wrapper ()
 {
-	start_of_thread (String::compose("Job-%1", json_name()));
+	start_of_thread(fmt::format("Job-{}", json_name()));
 
 	try {
 
@@ -113,7 +112,7 @@ Job::run_wrapper ()
 
 	} catch (dcp::FileError& e) {
 
-		string m = String::compose(_("An error occurred whilst handling the file %1."), e.filename().filename());
+		string m = fmt::format(_("An error occurred whilst handling the file {}."), e.filename().filename().string());
 
 		try {
 			auto const s = dcp::filesystem::space(e.filename());
@@ -138,9 +137,9 @@ Job::run_wrapper ()
 		/* 32-bit */
 		set_error (
 			_("Failed to encode the DCP."),
-			String::compose(
-				_("This error has probably occurred because you are running the 32-bit version of %1 and "
-				  "trying to use too many encoding threads.  Please reduce the 'number of threads %2 should "
+			fmt::format(
+				_("This error has probably occurred because you are running the 32-bit version of {} and "
+				  "trying to use too many encoding threads.  Please reduce the 'number of threads {} should "
 				  "use' in the General tab of Preferences and try again."),
 				variant::dcpomatic(),
 				variant::dcpomatic()
@@ -152,9 +151,9 @@ Job::run_wrapper ()
 		if (running_32_on_64()) {
 			set_error (
 				_("Failed to encode the DCP."),
-				String::compose(
-					_("This error has probably occurred because you are running the 32-bit version of %1.  "
-					  "Please re-install %2 with the 64-bit installer and try again."),
+				fmt::format(
+					_("This error has probably occurred because you are running the 32-bit version of {}.  "
+					  "Please re-install {} with the 64-bit installer and try again."),
 					variant::dcpomatic(),
 					variant::dcpomatic()
 					)
@@ -167,7 +166,7 @@ Job::run_wrapper ()
 		if (!done) {
 			set_error (
 				e.what (),
-				String::compose(_("It is not known what caused this error.  %1"), report_problem())
+				fmt::format(_("It is not known what caused this error.  {}"), report_problem())
 				);
 		}
 
@@ -177,8 +176,8 @@ Job::run_wrapper ()
 	} catch (OpenFileError& e) {
 
 		set_error (
-			String::compose (_("Could not open %1"), e.file().string()),
-			String::compose(_("%1 could not open the file %2 (%3).  Perhaps it does not exist or is in an unexpected format."),
+			fmt::format(_("Could not open {}"), e.file().string()),
+			fmt::format(_("{} could not open the file {} ({}).  Perhaps it does not exist or is in an unexpected format."),
 				variant::dcpomatic(),
 				dcp::filesystem::absolute(e.file()).string(),
 				e.what()
@@ -192,8 +191,8 @@ Job::run_wrapper ()
 
 		if (e.code() == boost::system::errc::no_such_file_or_directory) {
 			set_error (
-				String::compose (_("Could not open %1"), e.path1().string ()),
-				String::compose(_("%1 could not open the file %2 (%3).  Perhaps it does not exist or is in an unexpected format."),
+				fmt::format(_("Could not open {}"), e.path1().string()),
+				fmt::format(_("{} could not open the file {} ({}).  Perhaps it does not exist or is in an unexpected format."),
 					variant::dcpomatic(),
 					dcp::filesystem::absolute(e.path1()).string(),
 					e.what()
@@ -202,7 +201,7 @@ Job::run_wrapper ()
 		} else {
 			set_error (
 				e.what (),
-				String::compose(_("It is not known what caused this error.  %1"), report_problem())
+				fmt::format(_("It is not known what caused this error.  {}"), report_problem())
 				);
 		}
 
@@ -262,7 +261,7 @@ Job::run_wrapper ()
 
 		set_error (
 			e.what (),
-			String::compose(_("It is not known what caused this error.  %1"), report_problem())
+			fmt::format(_("It is not known what caused this error.  {}"), report_problem())
 			);
 
 		set_progress (1);
@@ -272,7 +271,7 @@ Job::run_wrapper ()
 
 		set_error (
 			_("Unknown error"),
-			String::compose(_("It is not known what caused this error.  %1"), report_problem())
+			fmt::format(_("It is not known what caused this error.  {}"), report_problem())
 			);
 
 		set_progress (1);
@@ -493,7 +492,7 @@ Job::sub (string n)
 {
 	{
 		boost::mutex::scoped_lock lm (_progress_mutex);
-		LOG_GENERAL ("Sub-job %1 starting", n);
+		LOG_GENERAL("Sub-job {} starting", n);
 		_sub_name = n;
 	}
 
@@ -527,7 +526,7 @@ void
 Job::set_error (string s, string d)
 {
 	if (_film) {
-		_film->log()->log (String::compose ("Error in job: %1 (%2)", s, d), LogEntry::TYPE_ERROR);
+		_film->log()->log(fmt::format("Error in job: {} ({})", s, d), LogEntry::TYPE_ERROR);
 	}
 
 	boost::mutex::scoped_lock lm (_state_mutex);
@@ -593,14 +592,14 @@ Job::status () const
 			snprintf (finish_string, sizeof(finish_string), "%02d:%02d", int(finish.time_of_day().hours()), int(finish.time_of_day().minutes()));
 			string day;
 			if (now.date() != finish.date()) {
-				/// TRANSLATORS: the %1 in this string will be filled in with a day of the week
+				/// TRANSLATORS: the {} in this string will be filled in with a day of the week
 				/// to say what day a job will finish.
-				day = String::compose (_(" on %1"), day_of_week_to_string(finish.date().day_of_week()));
+				day = fmt::format(_(" on {}"), day_of_week_to_string(finish.date().day_of_week()));
 			}
 			/// TRANSLATORS: "remaining; finishing at" here follows an amount of time that is remaining
 			/// on an operation; after it is an estimated wall-clock completion time.
-			s += String::compose(
-				_("; %1 remaining; finishing at %2%3"),
+			s += fmt::format(
+				_("; {} remaining; finishing at {}{}"),
 				seconds_to_approximate_hms(r), finish_string, day
 				);
 		}
@@ -617,12 +616,12 @@ Job::status () const
 			s = _("OK");
 		} else if (duration < 600) {
 			/* It took less than 10 minutes; it doesn't seem worth saying when it started and finished */
-			s = String::compose(_("OK (ran for %1)"), seconds_to_hms(duration));
+			s = fmt::format(_("OK (ran for {})"), seconds_to_hms(duration));
 		} else {
-			s = String::compose(_("OK (ran for %1 from %2 to %3)"),  seconds_to_hms(duration), time_string(_start_time), time_string(_finish_time));
+			s = fmt::format(_("OK (ran for {} from {} to {})"), seconds_to_hms(duration), time_string(_start_time), time_string(_finish_time));
 		}
 	} else if (finished_in_error ()) {
-		s = String::compose (_("Error: %1"), error_summary ());
+		s = fmt::format(_("Error: {}"), error_summary());
 	} else if (finished_cancelled ()) {
 		s = _("Cancelled");
 	}
diff --git a/src/lib/kdm_cli.cc b/src/lib/kdm_cli.cc
index 20cbf33e6..0d0c6a8b8 100644
--- a/src/lib/kdm_cli.cc
+++ b/src/lib/kdm_cli.cc
@@ -39,6 +39,7 @@
 #include <dcp/decrypted_kdm.h>
 #include <dcp/encrypted_kdm.h>
 #include <dcp/filesystem.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <getopt.h>
 
@@ -62,13 +63,13 @@ using namespace dcpomatic;
 static void
 help (std::function<void (string)> out)
 {
-	out (String::compose("Syntax: %1 [OPTION] [COMMAND] <FILM|CPL-ID|DKDM>", program_name));
+	out (fmt::format("Syntax: {} [OPTION] [COMMAND] <FILM|CPL-ID|DKDM>", program_name));
 	out ("Commands:");
 	out ("create          create KDMs; default if no other command is specified");
-	out (variant::insert_dcpomatic("list-cinemas                 list known cinemas from %1 settings"));
-	out (variant::insert_dcpomatic("list-dkdm-cpls               list CPLs for which %1 has DKDMs"));
-	out (variant::insert_dcpomatic("add-dkdm                     add DKDM to %1's list"));
-	out (variant::insert_dcpomatic("dump-decryption-certificate  write the %1 KDM decryption certificate to the console"));
+	out (variant::insert_dcpomatic("list-cinemas                 list known cinemas from {} settings"));
+	out (variant::insert_dcpomatic("list-dkdm-cpls               list CPLs for which {} has DKDMs"));
+	out (variant::insert_dcpomatic("add-dkdm                     add DKDM to {}'s list"));
+	out (variant::insert_dcpomatic("dump-decryption-certificate  write the {} KDM decryption certificate to the console"));
 	out ("  -h, --help                               show this help");
 	out ("  -o, --output <path>                      output file or directory");
 	out ("  -K, --filename-format <format>           filename format for KDMs");
@@ -87,17 +88,17 @@ help (std::function<void (string)> out)
 	out ("  -C, --projector-certificate <file>       file containing projector certificate");
 	out ("  -T, --trusted-device-certificate <file>  file containing a trusted device's certificate");
 	out ("      --decryption-key <file>              file containing the private key which can decrypt the given DKDM");
-	out (variant::insert_dcpomatic("                                           (%1's configured private key will be used otherwise)"));
+	out (variant::insert_dcpomatic("                                           ({}'s configured private key will be used otherwise)"));
 	out ("      --cinemas-file <file>                use the given file as a list of cinemas instead of the current configuration");
 	out ("");
-	out (variant::insert_dcpomatic("CPL-ID must be the ID of a CPL that is mentioned in %1's DKDM list."));
+	out (variant::insert_dcpomatic("CPL-ID must be the ID of a CPL that is mentioned in {}'s DKDM list."));
 	out ("");
 	out ("For example:");
 	out ("");
 	out ("Create KDMs for my_great_movie to play in all of Fred's Cinema's screens for the next two weeks and zip them up.");
-	out (variant::insert_dcpomatic("(Fred's Cinema must have been set up in %1's KDM window)"));
+	out (variant::insert_dcpomatic("(Fred's Cinema must have been set up in {}'s KDM window)"));
 	out ("");
-	out (String::compose("\t%1 -c \"Fred's Cinema\" -f now -d \"2 weeks\" -z my_great_movie", program_name));
+	out (fmt::format("\t{} -c \"Fred's Cinema\" -f now -d \"2 weeks\" -z my_great_movie", program_name));
 }
 
 
@@ -105,7 +106,7 @@ class KDMCLIError : public std::runtime_error
 {
 public:
 	KDMCLIError (std::string message)
-		: std::runtime_error (String::compose("%1: %2", program_name, message).c_str())
+		: std::runtime_error(fmt::format("{}: {}", program_name, message).c_str())
 	{}
 };
 
@@ -119,7 +120,7 @@ duration_from_string (string d)
 	string const unit (unit_buf);
 
 	if (N == 0) {
-		throw KDMCLIError (String::compose("could not understand duration \"%1\"", d));
+		throw KDMCLIError(fmt::format("could not understand duration \"{}\"", d));
 	}
 
 	if (unit == "year" || unit == "years") {
@@ -132,7 +133,7 @@ duration_from_string (string d)
 		return boost::posix_time::time_duration (N, 0, 0, 0);
 	}
 
-	throw KDMCLIError (String::compose("could not understand duration \"%1\"", d));
+	throw KDMCLIError(fmt::format("could not understand duration \"{}\"", d));
 }
 
 
@@ -165,7 +166,7 @@ write_files (
 			);
 
 		if (verbose) {
-			out (String::compose("Wrote %1 ZIP files to %2", N, output));
+			out(fmt::format("Wrote {} ZIP files to {}", N, output.string()));
 		}
 	} else {
 		int const N = write_files (
@@ -174,7 +175,7 @@ write_files (
 			);
 
 		if (verbose) {
-			out (String::compose("Wrote %1 KDM files to %2", N, output));
+			out(fmt::format("Wrote {} KDM files to {}", N, output.string()));
 		}
 	}
 }
@@ -219,10 +220,10 @@ from_film (
 		film = make_shared<Film>(film_dir);
 		film->read_metadata ();
 		if (verbose) {
-			out (String::compose("Read film %1", film->name()));
+			out(fmt::format("Read film {}", film->name()));
 		}
 	} catch (std::exception& e) {
-		throw KDMCLIError (String::compose("error reading film \"%1\" (%2)", film_dir.string(), e.what()));
+		throw KDMCLIError(fmt::format("error reading film \"{}\" ({})", film_dir.string(), e.what()));
 	}
 
 	/* XXX: allow specification of this */
@@ -283,7 +284,7 @@ from_film (
 			send_emails ({kdms}, container_name_format, filename_format, film->dcp_name(), {});
 		}
 	} catch (FileError& e) {
-		throw KDMCLIError (String::compose("%1 (%2)", e.what(), e.file().string()));
+		throw KDMCLIError(fmt::format("{} ({})", e.what(), e.file().string()));
 	}
 }
 
@@ -410,7 +411,7 @@ from_dkdm (
 			send_emails ({kdms}, container_name_format, filename_format, dkdm.annotation_text().get_value_or(""), {});
 		}
 	} catch (FileError& e) {
-		throw KDMCLIError (String::compose("%1 (%2)", e.what(), e.file().string()));
+		throw KDMCLIError(fmt::format("{} ({})", e.what(), e.file().string()));
 	}
 }
 
@@ -625,7 +626,7 @@ try
 	}
 
 	if (std::find(commands.begin(), commands.end(), command) == commands.end()) {
-		throw KDMCLIError(String::compose("Unrecognised command %1", command));
+		throw KDMCLIError(fmt::format("Unrecognised command {}", command));
 	}
 
 	if (cinemas_file) {
@@ -646,7 +647,7 @@ try
 	if (command == "list-cinemas") {
 		CinemaList cinemas;
 		for (auto const& cinema: cinemas.cinemas()) {
-			out(String::compose("%1 (%2)", cinema.second.name, Email::address_list(cinema.second.emails)));
+			out(fmt::format("{} ({})", cinema.second.name, Email::address_list(cinema.second.emails)));
 		}
 		return {};
 	}
@@ -714,7 +715,7 @@ try
 	}
 
 	if (verbose) {
-		out(String::compose("Making KDMs valid from %1 to %2", valid_from->as_string(), valid_to->as_string()));
+		out(fmt::format("Making KDMs valid from {} to {}", valid_from->as_string(), valid_to->as_string()));
 	}
 
 	string const thing = argv[optind];
diff --git a/src/lib/make_dcp.cc b/src/lib/make_dcp.cc
index b72756194..840fbf1a1 100644
--- a/src/lib/make_dcp.cc
+++ b/src/lib/make_dcp.cc
@@ -88,10 +88,10 @@ make_dcp (shared_ptr<Film> film, TranscodeJob::ChangedBehaviour behaviour)
 	}
 
 	for (auto content: film->content()) {
-		LOG_GENERAL ("Content: %1", content->technical_summary());
+		LOG_GENERAL("Content: {}", content->technical_summary());
 	}
-	LOG_GENERAL ("DCP video rate %1 fps", film->video_frame_rate());
-	LOG_GENERAL("Video bit rate %1", film->video_bit_rate(film->video_encoding()));
+	LOG_GENERAL("DCP video rate {} fps", film->video_frame_rate());
+	LOG_GENERAL("Video bit rate {}", film->video_bit_rate(film->video_encoding()));
 
 	auto tj = make_shared<DCPTranscodeJob>(film, behaviour);
 	tj->set_encoder(make_shared<DCPFilmEncoder>(film, tj));
diff --git a/src/lib/map_cli.cc b/src/lib/map_cli.cc
index 149e09fbc..034a4e2aa 100644
--- a/src/lib/map_cli.cc
+++ b/src/lib/map_cli.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "util.h"
 #include <dcp/cpl.h>
@@ -55,7 +54,7 @@ using boost::optional;
 static void
 help(std::function<void (string)> out)
 {
-	out(String::compose("Syntax: %1 [OPTION} <cpl-file|ID> [<cpl-file|ID> ... ]", program_name));
+	out(fmt::format("Syntax: {} [OPTION} <cpl-file|ID> [<cpl-file|ID> ... ]", program_name));
 	out("  -V, --version    show libdcp version");
 	out("  -h, --help       show this help");
 	out("  -o, --output     output directory");
@@ -151,7 +150,7 @@ map_cli(int argc, char* argv[], std::function<void (string)> out)
 	}
 
 	if (dcp::filesystem::exists(*output_dir)) {
-		return String::compose("Output directory %1 already exists.", *output_dir);
+		return fmt::format("Output directory {} already exists.", output_dir->string());
 	}
 
 	if (hard_link && soft_link) {
@@ -161,7 +160,7 @@ map_cli(int argc, char* argv[], std::function<void (string)> out)
 	boost::system::error_code ec;
 	dcp::filesystem::create_directory(*output_dir, ec);
 	if (ec) {
-		return String::compose("Could not create output directory %1: %2", *output_dir, ec.message());
+		return fmt::format("Could not create output directory {}: {}", output_dir->string(), ec.message());
 	}
 
 	/* Find all the assets in the asset directories.  This assumes that the asset directories are in fact
@@ -187,20 +186,20 @@ map_cli(int argc, char* argv[], std::function<void (string)> out)
 				cpl->resolve_refs(assets);
 				cpls.push_back(cpl);
 			} catch (std::exception& e) {
-				return String::compose("Could not read CPL %1: %2", filename_or_id, e.what());
+				return fmt::format("Could not read CPL {}: {}", filename_or_id, e.what());
 			}
 		} else {
 			auto cpl_iter = std::find_if(assets.begin(), assets.end(), [filename_or_id](shared_ptr<dcp::Asset> asset) {
 				return asset->id() == filename_or_id;
 			});
 			if (cpl_iter == assets.end()) {
-				return String::compose("Could not find CPL with ID %1", filename_or_id);
+				return fmt::format("Could not find CPL with ID {}", filename_or_id);
 			}
 			if (auto cpl = dynamic_pointer_cast<dcp::CPL>(*cpl_iter)) {
 				cpl->resolve_refs(assets);
 				cpls.push_back(cpl);
 			} else {
-				return String::compose("Could not find CPL with ID %1", filename_or_id);
+				return fmt::format("Could not find CPL with ID {}", filename_or_id);
 			}
 		}
 	}
@@ -225,17 +224,17 @@ map_cli(int argc, char* argv[], std::function<void (string)> out)
 		if (hard_link) {
 			dcp::filesystem::create_hard_link(input_path, output_path, ec);
 			if (ec) {
-				throw CopyError(String::compose("Could not hard-link asset %1: %2", input_path.string(), ec.message()));
+				throw CopyError(fmt::format("Could not hard-link asset {}: {}", input_path.string(), ec.message()));
 			}
 		} else if (soft_link) {
 			dcp::filesystem::create_symlink(input_path, output_path, ec);
 			if (ec) {
-				throw CopyError(String::compose("Could not soft-link asset %1: %2", input_path.string(), ec.message()));
+				throw CopyError(fmt::format("Could not soft-link asset {}: {}", input_path.string(), ec.message()));
 			}
 		} else {
 			dcp::filesystem::copy_file(input_path, output_path, ec);
 			if (ec) {
-				throw CopyError(String::compose("Could not copy asset %1: %2", input_path.string(), ec.message()));
+				throw CopyError(fmt::format("Could not copy asset {}: {}", input_path.string(), ec.message()));
 			}
 		}
 	};
@@ -263,7 +262,7 @@ map_cli(int argc, char* argv[], std::function<void (string)> out)
 			}
 
 			if (rename) {
-				output_path /= String::compose("%1%2", (*iter)->id(), dcp::filesystem::extension((*iter)->file().get()));
+				output_path /= fmt::format("{}{}", (*iter)->id(), dcp::filesystem::extension((*iter)->file().get()));
 				(*iter)->rename_file(output_path);
 			} else {
 				output_path /= (*iter)->file()->filename();
@@ -275,7 +274,7 @@ map_cli(int argc, char* argv[], std::function<void (string)> out)
 		} else {
 			boost::system::error_code ec;
 			dcp::filesystem::remove_all(*output_dir, ec);
-			throw CopyError(String::compose("Could not find required asset %1", asset_id));
+			throw CopyError(fmt::format("Could not find required asset {}", asset_id));
 		}
 	};
 
@@ -339,7 +338,7 @@ map_cli(int argc, char* argv[], std::function<void (string)> out)
 		dcp.set_issuer(Config::instance()->dcp_issuer());
 		dcp.write_xml(Config::instance()->signer_chain());
 	} catch (dcp::UnresolvedRefError& e) {
-		return String::compose("%1\nPerhaps you need to give a -d parameter to say where this asset is located.", e.what());
+		return fmt::format("{}\nPerhaps you need to give a -d parameter to say where this asset is located.", e.what());
 	}
 
 	return {};
diff --git a/src/lib/nanomsg.cc b/src/lib/nanomsg.cc
index 8061e2f84..8c439f36e 100644
--- a/src/lib/nanomsg.cc
+++ b/src/lib/nanomsg.cc
@@ -22,6 +22,7 @@
 #include "dcpomatic_log.h"
 #include "exceptions.h"
 #include "nanomsg.h"
+#include <fmt/format.h>
 #include <nanomsg/nn.h>
 #include <nanomsg/pair.h>
 #include <cerrno>
@@ -44,11 +45,11 @@ Nanomsg::Nanomsg (bool server)
 	}
 	if (server) {
 		if ((_endpoint = nn_bind(_socket, NANOMSG_URL)) < 0) {
-			throw runtime_error(String::compose("Could not bind nanomsg socket (%1)", errno));
+			throw runtime_error(fmt::format("Could not bind nanomsg socket ({})", errno));
 		}
 	} else {
 		if ((_endpoint = nn_connect(_socket, NANOMSG_URL)) < 0) {
-			throw runtime_error(String::compose("Could not connect nanomsg socket (%1)", errno));
+			throw runtime_error(fmt::format("Could not connect nanomsg socket ({})", errno));
 		}
 	}
 }
@@ -73,7 +74,7 @@ Nanomsg::send (string s, int timeout)
 		if (errno == ETIMEDOUT || errno == EAGAIN) {
 			return false;
 		}
-		throw runtime_error(String::compose("Could not send to nanomsg socket (%1)", errno));
+		throw runtime_error(fmt::format("Could not send to nanomsg socket ({})", errno));
 	} else if (r != int(s.length())) {
 		throw runtime_error("Could not send to nanomsg socket (message too big)");
 	}
diff --git a/src/lib/player.cc b/src/lib/player.cc
index f348f6b28..3c8da9955 100644
--- a/src/lib/player.cc
+++ b/src/lib/player.cc
@@ -24,7 +24,6 @@
 #include "audio_content.h"
 #include "audio_decoder.h"
 #include "audio_processor.h"
-#include "compose.hpp"
 #include "config.h"
 #include "content_audio.h"
 #include "content_video.h"
@@ -57,6 +56,7 @@
 #include <dcp/reel_picture_asset.h>
 #include <dcp/reel_sound_asset.h>
 #include <dcp/reel_text_asset.h>
+#include <fmt/format.h>
 #include <algorithm>
 #include <iostream>
 #include <stdint.h>
@@ -768,7 +768,7 @@ Player::pass ()
 	switch (which) {
 	case CONTENT:
 	{
-		LOG_DEBUG_PLAYER ("Calling pass() on %1", earliest_content->content->path(0));
+		LOG_DEBUG_PLAYER("Calling pass() on {}", earliest_content->content->path(0).string());
 		earliest_content->done = earliest_content->decoder->pass ();
 		auto dcp = dynamic_pointer_cast<DCPContent>(earliest_content->content);
 		if (dcp && !_play_referenced) {
@@ -786,7 +786,7 @@ Player::pass ()
 		break;
 	}
 	case BLACK:
-		LOG_DEBUG_PLAYER ("Emit black for gap at %1", to_string(_black.position()));
+		LOG_DEBUG_PLAYER("Emit black for gap at {}", to_string(_black.position()));
 		if (!_next_video_time) {
 			/* Deciding to emit black has the same effect as getting some video from the content
 			 * when we are inaccurately seeking.
@@ -803,7 +803,7 @@ Player::pass ()
 		break;
 	case SILENT:
 	{
-		LOG_DEBUG_PLAYER ("Emit silence for gap at %1", to_string(_silent.position()));
+		LOG_DEBUG_PLAYER("Emit silence for gap at {}", to_string(_silent.position()));
 		DCPTimePeriod period (_silent.period_at_position());
 		if (_next_audio_time) {
 			/* Sometimes the thing that happened last finishes fractionally before
@@ -815,7 +815,7 @@ Player::pass ()
 			/* Let's not worry about less than a frame at 24fps */
 			int64_t const too_much_error = DCPTime::from_frames(1, 24).get();
 			if (error >= too_much_error) {
-				film->log()->log(String::compose("Silence starting before or after last audio by %1", error), LogEntry::TYPE_ERROR);
+				film->log()->log(fmt::format("Silence starting before or after last audio by {}", error), LogEntry::TYPE_ERROR);
 			}
 			DCPOMATIC_ASSERT (error < too_much_error);
 			period.from = *_next_audio_time;
@@ -858,14 +858,18 @@ Player::pass ()
 	std::map<AudioStreamPtr, StreamState> alive_stream_states;
 
 	if (latest_last_push_end != have_pushed.end()) {
-		LOG_DEBUG_PLAYER("Leading audio stream is in %1 at %2", latest_last_push_end->second.piece->content->path(0), to_string(latest_last_push_end->second.last_push_end.get()));
+		LOG_DEBUG_PLAYER(
+			"Leading audio stream is in {} at {}",
+			latest_last_push_end->second.piece->content->path(0).string(),
+			to_string(latest_last_push_end->second.last_push_end.get())
+			);
 
 		/* Now make a list of those streams that are less than ignore_streams_behind behind the leader */
 		for (auto const& i: _stream_states) {
 			if (!i.second.last_push_end || (latest_last_push_end->second.last_push_end.get() - i.second.last_push_end.get()) < dcpomatic::DCPTime::from_seconds(ignore_streams_behind)) {
 				alive_stream_states.insert(i);
 			} else {
-				LOG_DEBUG_PLAYER("Ignoring stream %1 because it is too far behind", i.second.piece->content->path(0));
+				LOG_DEBUG_PLAYER("Ignoring stream {} because it is too far behind", i.second.piece->content->path(0).string());
 			}
 		}
 	}
@@ -881,7 +885,7 @@ Player::pass ()
 		pull_to = _silent.position();
 	}
 
-	LOG_DEBUG_PLAYER("Emitting audio up to %1", to_string(pull_to));
+	LOG_DEBUG_PLAYER("Emitting audio up to {}", to_string(pull_to));
 	auto audio = _audio_merger.pull (pull_to);
 	for (auto i = audio.begin(); i != audio.end(); ++i) {
 		if (_next_audio_time && i->second < *_next_audio_time) {
@@ -901,7 +905,7 @@ Player::pass ()
 
 	if (done) {
 		if (_next_video_time) {
-			LOG_DEBUG_PLAYER("Done: emit video until end of film at %1", to_string(film->length()));
+			LOG_DEBUG_PLAYER("Done: emit video until end of film at {}", to_string(film->length()));
 			emit_video_until(film->length());
 		}
 
@@ -977,7 +981,7 @@ Player::open_texts_for_frame(DCPTime time) const
 void
 Player::emit_video_until(DCPTime time)
 {
-	LOG_DEBUG_PLAYER("emit_video_until %1; next video time is %2", to_string(time), to_string(_next_video_time.get_value_or({})));
+	LOG_DEBUG_PLAYER("emit_video_until {}; next video time is {}", to_string(time), to_string(_next_video_time.get_value_or({})));
 	auto frame = [this](shared_ptr<PlayerVideo> pv, DCPTime time) {
 		/* We need a delay to give a little wiggle room to ensure that relevant subtitles arrive at the
 		   player before the video that requires them.
@@ -1017,7 +1021,7 @@ Player::emit_video_until(DCPTime time)
 			frame(right.first, next);
 		} else if (both.first && (both.second - next) < age_threshold) {
 			frame(both.first, next);
-			LOG_DEBUG_PLAYER("Content %1 selected for DCP %2 (age %3)", to_string(both.second), to_string(next), to_string(both.second - next));
+			LOG_DEBUG_PLAYER("Content {} selected for DCP {} (age {})", to_string(both.second), to_string(next), to_string(both.second - next));
 		} else {
 			auto film = _film.lock();
 			if (film && film->three_d()) {
@@ -1026,7 +1030,7 @@ Player::emit_video_until(DCPTime time)
 			} else {
 				frame(black_player_video_frame(Eyes::BOTH), next);
 			}
-			LOG_DEBUG_PLAYER("Black selected for DCP %1", to_string(next));
+			LOG_DEBUG_PLAYER("Black selected for DCP {}", to_string(next));
 		}
 	}
 }
@@ -1077,7 +1081,7 @@ Player::video (weak_ptr<Piece> weak_piece, ContentVideo video)
 
 	/* Time of the frame we just received within the DCP */
 	auto const time = content_time_to_dcp(piece, video.time);
-	LOG_DEBUG_PLAYER("Received video frame %1 %2 eyes %3", to_string(video.time), to_string(time), static_cast<int>(video.eyes));
+	LOG_DEBUG_PLAYER("Received video frame {} {} eyes {}", to_string(video.time), to_string(time), static_cast<int>(video.eyes));
 
 	if (time < piece->content->position()) {
 		return;
@@ -1167,7 +1171,7 @@ Player::audio (weak_ptr<Piece> weak_piece, AudioStreamPtr stream, ContentAudio c
 
 	/* And the end of this block in the DCP */
 	auto end = time + DCPTime::from_frames(content_audio.audio->frames(), rfr);
-	LOG_DEBUG_PLAYER("Received audio frame %1 covering %2 to %3 (%4)", content_audio.frame, to_string(time), to_string(end), piece->content->path(0).filename());
+	LOG_DEBUG_PLAYER("Received audio frame {} covering {} to {} ({})", content_audio.frame, to_string(time), to_string(end), piece->content->path(0).filename().string());
 
 	/* Remove anything that comes before the start or after the end of the content */
 	if (time < piece->content->position()) {
@@ -1369,7 +1373,7 @@ void
 Player::seek (DCPTime time, bool accurate)
 {
 	boost::mutex::scoped_lock lm (_mutex);
-	LOG_DEBUG_PLAYER("Seek to %1 (%2accurate)", to_string(time), accurate ? "" : "in");
+	LOG_DEBUG_PLAYER("Seek to {} ({}accurate)", to_string(time), accurate ? "" : "in");
 
 	if (_suspended) {
 		/* We can't seek in this state */
@@ -1457,7 +1461,7 @@ Player::emit_audio (shared_ptr<AudioBuffers> data, DCPTime time)
 
 	/* Log if the assert below is about to fail */
 	if (_next_audio_time && labs(time.get() - _next_audio_time->get()) > 1) {
-		film->log()->log(String::compose("Out-of-sequence emit %1 vs %2", to_string(time), to_string(*_next_audio_time)), LogEntry::TYPE_WARNING);
+		film->log()->log(fmt::format("Out-of-sequence emit {} vs {}", to_string(time), to_string(*_next_audio_time)), LogEntry::TYPE_WARNING);
 	}
 
 	/* This audio must follow on from the previous, allowing for half a sample (at 48kHz) leeway */
diff --git a/src/lib/playlist.cc b/src/lib/playlist.cc
index a0d7d6531..92871f8b0 100644
--- a/src/lib/playlist.cc
+++ b/src/lib/playlist.cc
@@ -20,7 +20,6 @@
 
 
 #include "audio_content.h"
-#include "compose.hpp"
 #include "config.h"
 #include "content_factory.h"
 #include "dcp_content.h"
@@ -36,6 +35,7 @@
 #include "video_content.h"
 #include <libcxml/cxml.h>
 #include <libxml++/libxml++.h>
+#include <fmt/format.h>
 #include <boost/bind/placeholders.hpp>
 #include <iostream>
 
@@ -236,13 +236,13 @@ Playlist::set_from_xml (shared_ptr<const Film> film, cxml::ConstNodePtr node, in
 			string note = _("Your project contains video content that was not aligned to a frame boundary.");
 			note += "  ";
 			if (old_pos < content->position()) {
-				note += String::compose(
-					_("The file %1 has been moved %2 milliseconds later."),
+				note += fmt::format(
+					_("The file {} has been moved {} milliseconds later."),
 					content->path_summary(), DCPTime(content->position() - old_pos).seconds() * 1000
 					);
 			} else {
-				note += String::compose(
-					_("The file %1 has been moved %2 milliseconds earlier."),
+				note += fmt::format(
+					_("The file {} has been moved {} milliseconds earlier."),
 					content->path_summary(), DCPTime(content->position() - old_pos).seconds() * 1000
 					);
 			}
@@ -256,13 +256,13 @@ Playlist::set_from_xml (shared_ptr<const Film> film, cxml::ConstNodePtr node, in
 			string note = _("Your project contains video content whose trim was not aligned to a frame boundary.");
 			note += "  ";
 			if (old_trim < content->trim_start()) {
-				note += String::compose(
-					_("The file %1 has been trimmed by %2 milliseconds more."),
+				note += fmt::format(
+					_("The file {} has been trimmed by {} milliseconds more."),
 					content->path_summary(), ContentTime(content->trim_start() - old_trim).seconds() * 1000
 					);
 			} else {
-				note += String::compose(
-					_("The file %1 has been trimmed by %2 milliseconds less."),
+				note += fmt::format(
+					_("The file {} has been trimmed by {} milliseconds less."),
 					content->path_summary(), ContentTime(old_trim - content->trim_start()).seconds() * 1000
 					);
 			}
diff --git a/src/lib/raw_image_proxy.cc b/src/lib/raw_image_proxy.cc
index 996cdc65f..9e819140b 100644
--- a/src/lib/raw_image_proxy.cc
+++ b/src/lib/raw_image_proxy.cc
@@ -30,6 +30,7 @@ extern "C" {
 LIBDCP_DISABLE_WARNINGS
 #include <libxml++/libxml++.h>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 
 #include "i18n.h"
 
diff --git a/src/lib/reel_writer.cc b/src/lib/reel_writer.cc
index f8694c5d3..7dbf16a02 100644
--- a/src/lib/reel_writer.cc
+++ b/src/lib/reel_writer.cc
@@ -20,7 +20,6 @@
 
 
 #include "audio_buffers.h"
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "cross.h"
@@ -164,7 +163,7 @@ ReelWriter::ReelWriter (
 
 		auto new_asset_filename = _output_dir / video_asset_filename(picture_asset, _reel_index, _reel_count, _content_summary);
 		if (_first_nonexistent_frame > 0) {
-			LOG_GENERAL("Re-using partial asset %1: has frames up to %2", *existing_asset_filename, _first_nonexistent_frame);
+			LOG_GENERAL("Re-using partial asset {}: has frames up to {}", existing_asset_filename->string(), _first_nonexistent_frame);
 			dcp::filesystem::rename(*existing_asset_filename, new_asset_filename);
 		}
 		remembered_assets.push_back(RememberedAsset(new_asset_filename.filename(), period, film()->video_identifier()));
@@ -178,7 +177,7 @@ ReelWriter::ReelWriter (
 			_mpeg2_picture_asset_writer = _mpeg2_picture_asset->start_write(new_asset_filename, behaviour);
 		}
 	} else {
-		LOG_GENERAL("Re-using complete asset %1", *existing_asset_filename);
+		LOG_GENERAL("Re-using complete asset {}", existing_asset_filename->string());
 		/* We already have a complete picture asset that we can just re-use */
 		/* XXX: what about if the encryption key changes? */
 		auto new_asset_filename = _output_dir / existing_asset_filename->filename();
@@ -249,10 +248,10 @@ ReelWriter::check_existing_picture_asset (boost::filesystem::path asset)
 	/* Try to open the existing asset */
 	dcp::File asset_file(asset, "rb");
 	if (!asset_file) {
-		LOG_GENERAL ("Could not open existing asset at %1 (errno=%2)", asset.string(), errno);
+		LOG_GENERAL("Could not open existing asset at {} (errno={})", asset.string(), errno);
 		return 0;
 	} else {
-		LOG_GENERAL ("Opened existing asset at %1", asset.string());
+		LOG_GENERAL("Opened existing asset at {}", asset.string());
 	}
 
 	shared_ptr<InfoFileHandle> info_file;
@@ -266,7 +265,7 @@ ReelWriter::check_existing_picture_asset (boost::filesystem::path asset)
 
 	/* Offset of the last dcp::FrameInfo in the info file */
 	int const n = (dcp::filesystem::file_size(info_file->get().path()) / J2KFrameInfo::size_on_disk()) - 1;
-	LOG_GENERAL("The last FI is %1; info file is %2, info size %3", n, dcp::filesystem::file_size(info_file->get().path()), J2KFrameInfo::size_on_disk())
+	LOG_GENERAL("The last FI is {}; info file is {}, info size {}", n, dcp::filesystem::file_size(info_file->get().path()), J2KFrameInfo::size_on_disk())
 
 	Frame first_nonexistent_frame;
 	if (film()->three_d()) {
@@ -287,7 +286,7 @@ ReelWriter::check_existing_picture_asset (boost::filesystem::path asset)
 		++first_nonexistent_frame;
 	}
 
-	LOG_GENERAL ("Proceeding with first nonexistent frame %1", first_nonexistent_frame);
+	LOG_GENERAL("Proceeding with first nonexistent frame {}", first_nonexistent_frame);
 
 	return first_nonexistent_frame;
 }
@@ -360,13 +359,13 @@ ReelWriter::finish (boost::filesystem::path output_dcp)
 {
 	if (_j2k_picture_asset_writer && !_j2k_picture_asset_writer->finalize()) {
 		/* Nothing was written to the J2K picture asset */
-		LOG_GENERAL("Nothing was written to J2K asset for reel %1 of %2", _reel_index, _reel_count);
+		LOG_GENERAL("Nothing was written to J2K asset for reel {} of {}", _reel_index, _reel_count);
 		_j2k_picture_asset.reset();
 	}
 
 	if (_mpeg2_picture_asset_writer && !_mpeg2_picture_asset_writer->finalize()) {
 		/* Nothing was written to the MPEG2 picture asset */
-		LOG_GENERAL("Nothing was written to MPEG2 asset for reel %1 of %2", _reel_index, _reel_count);
+		LOG_GENERAL("Nothing was written to MPEG2 asset for reel {} of {}", _reel_index, _reel_count);
 		_mpeg2_picture_asset.reset();
 	}
 
@@ -385,7 +384,7 @@ ReelWriter::finish (boost::filesystem::path output_dcp)
 		dcp::filesystem::rename(film()->file(aaf), audio_to, ec);
 		if (ec) {
 			throw FileError (
-				String::compose(_("could not move audio asset into the DCP (%1)"), error_details(ec)), aaf
+				fmt::format(_("could not move audio asset into the DCP ({})"), error_details(ec)), aaf
 				);
 		}
 
@@ -402,7 +401,7 @@ ReelWriter::finish (boost::filesystem::path output_dcp)
 		dcp::filesystem::rename(film()->file(aaf), atmos_to, ec);
 		if (ec) {
 			throw FileError (
-				String::compose(_("could not move atmos asset into the DCP (%1)"), error_details(ec)), aaf
+				fmt::format(_("could not move atmos asset into the DCP ({})"), error_details(ec)), aaf
 				);
 		}
 
@@ -484,7 +483,7 @@ maybe_add_text (
 		if (!text_only && reel_asset->actual_duration() != period_duration) {
 			throw ProgrammingError (
 				__FILE__, __LINE__,
-				String::compose ("%1 vs %2", reel_asset->actual_duration(), period_duration)
+				fmt::format("{} vs {}", reel_asset->actual_duration(), period_duration)
 				);
 		}
 		reel->add (reel_asset);
@@ -511,12 +510,12 @@ ReelWriter::create_reel_picture (shared_ptr<dcp::Reel> reel, list<ReferencedReel
 	} else if (_mpeg2_picture_asset) {
 		reel_asset = make_shared<dcp::ReelMonoPictureAsset>(_mpeg2_picture_asset, 0);
 	} else {
-		LOG_GENERAL ("no picture asset of our own; look through %1", refs.size());
+		LOG_GENERAL("no picture asset of our own; look through {}", refs.size());
 		/* We don't have a picture asset of our own; hopefully we have one to reference */
 		for (auto j: refs) {
 			auto k = dynamic_pointer_cast<dcp::ReelPictureAsset> (j.asset);
 			if (k) {
-				LOG_GENERAL ("candidate picture asset period is %1-%2", j.period.from.get(), j.period.to.get());
+				LOG_GENERAL("candidate picture asset period is {}-{}", j.period.from.get(), j.period.to.get());
 			}
 			if (k && j.period == _period) {
 				reel_asset = k;
@@ -530,7 +529,7 @@ ReelWriter::create_reel_picture (shared_ptr<dcp::Reel> reel, list<ReferencedReel
 	if (reel_asset->duration() != period_duration) {
 		throw ProgrammingError (
 			__FILE__, __LINE__,
-			String::compose ("%1 vs %2", reel_asset->actual_duration(), period_duration)
+			fmt::format("{} vs {}", reel_asset->actual_duration(), period_duration)
 			);
 	}
 	reel->add (reel_asset);
@@ -553,12 +552,12 @@ ReelWriter::create_reel_sound (shared_ptr<dcp::Reel> reel, list<ReferencedReelAs
 		/* We have made a sound asset of our own.  Put it into the reel */
 		reel_asset = make_shared<dcp::ReelSoundAsset>(_sound_asset, 0);
 	} else {
-		LOG_GENERAL ("no sound asset of our own; look through %1", refs.size());
+		LOG_GENERAL("no sound asset of our own; look through {}", refs.size());
 		/* We don't have a sound asset of our own; hopefully we have one to reference */
 		for (auto j: refs) {
 			auto k = dynamic_pointer_cast<dcp::ReelSoundAsset> (j.asset);
 			if (k) {
-				LOG_GENERAL ("candidate sound asset period is %1-%2", j.period.from.get(), j.period.to.get());
+				LOG_GENERAL("candidate sound asset period is {}-{}", j.period.from.get(), j.period.to.get());
 			}
 			if (k && j.period == _period) {
 				reel_asset = k;
@@ -574,15 +573,15 @@ ReelWriter::create_reel_sound (shared_ptr<dcp::Reel> reel, list<ReferencedReelAs
 
 	DCPOMATIC_ASSERT (reel_asset);
 	if (reel_asset->actual_duration() != period_duration) {
-		LOG_ERROR (
-			"Reel sound asset has length %1 but reel period is %2",
+		LOG_ERROR(
+			"Reel sound asset has length {} but reel period is {}",
 			reel_asset->actual_duration(),
 			period_duration
 			);
 		if (reel_asset->actual_duration() != period_duration) {
 			throw ProgrammingError (
 				__FILE__, __LINE__,
-				String::compose ("%1 vs %2", reel_asset->actual_duration(), period_duration)
+				fmt::format("{} vs {}", reel_asset->actual_duration(), period_duration)
 				);
 		}
 
@@ -703,7 +702,7 @@ ReelWriter::create_reel (
 	set<DCPTextTrack> ensure_closed_captions
 	)
 {
-	LOG_GENERAL ("create_reel for %1-%2; %3 of %4", _period.from.get(), _period.to.get(), _reel_index, _reel_count);
+	LOG_GENERAL("create_reel for {}-{}; {} of {}", _period.from.get(), _period.to.get(), _reel_index, _reel_count);
 
 	auto reel = make_shared<dcp::Reel>();
 
@@ -967,7 +966,7 @@ ReelWriter::write(PlayerText subs, TextType type, optional<DCPTextTrack> track,
 bool
 ReelWriter::existing_picture_frame_ok (dcp::File& asset_file, shared_ptr<InfoFileHandle> info_file, Frame frame) const
 {
-	LOG_GENERAL ("Checking existing picture frame %1", frame);
+	LOG_GENERAL("Checking existing picture frame {}", frame);
 
 	/* Read the data from the info file; for 3D we just check the left
 	   frames until we find a good one.
@@ -980,16 +979,16 @@ ReelWriter::existing_picture_frame_ok (dcp::File& asset_file, shared_ptr<InfoFil
 	asset_file.seek(info.offset, SEEK_SET);
 	ArrayData data (info.size);
 	size_t const read = asset_file.read(data.data(), 1, data.size());
-	LOG_GENERAL ("Read %1 bytes of asset data; wanted %2", read, info.size);
+	LOG_GENERAL("Read {} bytes of asset data; wanted {}", read, info.size);
 	if (read != static_cast<size_t> (data.size ())) {
-		LOG_GENERAL ("Existing frame %1 is incomplete", frame);
+		LOG_GENERAL("Existing frame {} is incomplete", frame);
 		ok = false;
 	} else {
 		Digester digester;
 		digester.add (data.data(), data.size());
-		LOG_GENERAL ("Hash %1 vs %2", digester.get(), info.hash);
+		LOG_GENERAL("Hash {} vs {}", digester.get(), info.hash);
 		if (digester.get() != info.hash) {
-			LOG_GENERAL ("Existing frame %1 failed hash check", frame);
+			LOG_GENERAL("Existing frame {} failed hash check", frame);
 			ok = false;
 		}
 	}
diff --git a/src/lib/release_notes.cc b/src/lib/release_notes.cc
index 64556bb26..58461f120 100644
--- a/src/lib/release_notes.cc
+++ b/src/lib/release_notes.cc
@@ -24,6 +24,7 @@
 #include "variant.h"
 #include "version.h"
 #include <dcp/raw_convert.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 
 #include "i18n.h"
@@ -93,9 +94,9 @@ find_release_notes(bool dark, optional<string> current)
 	}
 
 	string const colour = dark ? "white" : "black";
-	auto const span = String::compose("<span style=\"color: %1\">", colour);
+	auto const span = fmt::format("<span style=\"color: {}\">", colour);
 
-	auto output = String::compose("<h1>%1%2 %3 release notes</span></h1><ul>", span, variant::dcpomatic(), *current);
+	auto output = fmt::format("<h1>{}{} {} release notes</span></h1><ul>", span, variant::dcpomatic(), *current);
 
 	for (auto const& note: notes) {
 		output += string("<li>") + span + note + "</span>";
diff --git a/src/lib/remembered_asset.cc b/src/lib/remembered_asset.cc
index cc3d93edf..dfe0917c5 100644
--- a/src/lib/remembered_asset.cc
+++ b/src/lib/remembered_asset.cc
@@ -53,8 +53,8 @@ RememberedAsset::as_xml(xmlpp::Element* parent) const
 {
 	cxml::add_text_child(parent, "Filename", _filename.string());
 	auto period_node = cxml::add_child(parent, "Period");
-	cxml::add_text_child(period_node, "From", dcp::fmt::to_string(_period.from.get()));
-	cxml::add_text_child(period_node, "To", dcp::fmt::to_string(_period.to.get()));
+	cxml::add_text_child(period_node, "From", fmt::to_string(_period.from.get()));
+	cxml::add_text_child(period_node, "To", fmt::to_string(_period.to.get()));
 	cxml::add_text_child(parent, "Identifier", _identifier);
 }
 
diff --git a/src/lib/remote_j2k_encoder_thread.cc b/src/lib/remote_j2k_encoder_thread.cc
index 49d80953d..51d3e3207 100644
--- a/src/lib/remote_j2k_encoder_thread.cc
+++ b/src/lib/remote_j2k_encoder_thread.cc
@@ -44,7 +44,7 @@ void
 RemoteJ2KEncoderThread::log_thread_start() const
 {
 	start_of_thread("RemoteJ2KEncoder");
-	LOG_TIMING("start-encoder-thread thread=%1 server=%2", thread_id(), _server.host_name());
+	LOG_TIMING("start-encoder-thread thread={} server={}", thread_id(), _server.host_name());
 }
 
 
@@ -56,17 +56,17 @@ RemoteJ2KEncoderThread::encode(DCPVideo const& frame)
 	try {
 		encoded = make_shared<dcp::ArrayData>(frame.encode_remotely(_server));
 		if (_remote_backoff > 0) {
-			LOG_GENERAL("%1 was lost, but now she is found; removing backoff", _server.host_name());
+			LOG_GENERAL("{} was lost, but now she is found; removing backoff", _server.host_name());
 			_remote_backoff = 0;
 		}
 	} catch (std::exception& e) {
 		LOG_ERROR(
-			N_("Remote encode of %1 on %2 failed (%3); thread sleeping for %4s"),
+			N_("Remote encode of {} on {} failed ({}); thread sleeping for {}s"),
 			frame.index(), _server.host_name(), e.what(), _remote_backoff
 		);
 	} catch (...) {
 		LOG_ERROR(
-			N_("Remote encode of %1 on %2 failed; thread sleeping for %4s"),
+			N_("Remote encode of {} on {} failed; thread sleeping for {}s"),
 			frame.index(), _server.host_name(), _remote_backoff
 		);
 	}
diff --git a/src/lib/resampler.cc b/src/lib/resampler.cc
index 2c6594a6d..c2b75e1d5 100644
--- a/src/lib/resampler.cc
+++ b/src/lib/resampler.cc
@@ -22,8 +22,8 @@
 #include "resampler.h"
 #include "audio_buffers.h"
 #include "exceptions.h"
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
+#include <fmt/format.h>
 #include <samplerate.h>
 #include <iostream>
 #include <cmath>
@@ -51,7 +51,7 @@ Resampler::Resampler (int in, int out, int channels)
 	int error;
 	_src = src_new (SRC_SINC_BEST_QUALITY, _channels, &error);
 	if (!_src) {
-		throw runtime_error (String::compose(N_("could not create sample-rate converter (%1)"), error));
+		throw runtime_error (fmt::format(N_("could not create sample-rate converter ({})"), error));
 	}
 }
 
@@ -73,7 +73,7 @@ Resampler::set_fast ()
 	int error;
 	_src = src_new (SRC_LINEAR, _channels, &error);
 	if (!_src) {
-		throw runtime_error (String::compose(N_("could not create sample-rate converter (%1)"), error));
+		throw runtime_error (fmt::format(N_("could not create sample-rate converter ({})"), error));
 	}
 }
 
@@ -119,8 +119,8 @@ Resampler::run (shared_ptr<const AudioBuffers> in)
 		int const r = src_process (_src, &data);
 		if (r) {
 			throw EncodeError (
-				String::compose (
-					N_("could not run sample-rate converter (%1) [processing %2 to %3, %4 channels]"),
+				fmt::format (
+					N_("could not run sample-rate converter ({}) [processing {} to {}, {} channels]"),
 					src_strerror (r),
 					in_frames,
 					max_resampled_frames,
@@ -174,7 +174,7 @@ Resampler::flush ()
 
 	int const r = src_process (_src, &data);
 	if (r) {
-		throw EncodeError (String::compose(N_("could not run sample-rate converter (%1)"), src_strerror(r)));
+		throw EncodeError(fmt::format(N_("could not run sample-rate converter ({})"), src_strerror(r)));
 	}
 
 	out->set_frames (out_offset + data.output_frames_gen);
diff --git a/src/lib/scp_uploader.cc b/src/lib/scp_uploader.cc
index 6c63a6c3e..17577529a 100644
--- a/src/lib/scp_uploader.cc
+++ b/src/lib/scp_uploader.cc
@@ -24,7 +24,6 @@
 #include "job.h"
 #include "config.h"
 #include "cross.h"
-#include "compose.hpp"
 #include <dcp/file.h>
 #include <dcp/filesystem.h>
 #include <dcp/warnings.h>
@@ -44,7 +43,7 @@ SCPUploader::SCPUploader (function<void (string)> set_status, function<void (flo
 {
 	_session = ssh_new ();
 	if (!_session) {
-		throw NetworkError (String::compose(_("SSH error [%1]"), "ssh_new"));
+		throw NetworkError(fmt::format(_("SSH error [{}]"), "ssh_new"));
 	}
 
 	ssh_options_set (_session, SSH_OPTIONS_HOST, Config::instance()->tms_ip().c_str());
@@ -54,33 +53,33 @@ SCPUploader::SCPUploader (function<void (string)> set_status, function<void (flo
 
 	int r = ssh_connect (_session);
 	if (r != SSH_OK) {
-		throw NetworkError (String::compose(_("Could not connect to server %1 (%2)"), Config::instance()->tms_ip(), ssh_get_error(_session)));
+		throw NetworkError(fmt::format(_("Could not connect to server {} ({})"), Config::instance()->tms_ip(), ssh_get_error(_session)));
 	}
 
 LIBDCP_DISABLE_WARNINGS
 	r = ssh_is_server_known (_session);
 	if (r == SSH_SERVER_ERROR) {
-		throw NetworkError (String::compose(_("SSH error [%1] (%2)"), "ssh_is_server_known", ssh_get_error(_session)));
+		throw NetworkError(fmt::format(_("SSH error [{}] ({})"), "ssh_is_server_known", ssh_get_error(_session)));
 	}
 LIBDCP_ENABLE_WARNINGS
 
 	r = ssh_userauth_password (_session, 0, Config::instance()->tms_password().c_str ());
 	if (r != SSH_AUTH_SUCCESS) {
-		throw NetworkError (String::compose(_("Failed to authenticate with server (%1)"), ssh_get_error(_session)));
+		throw NetworkError(fmt::format(_("Failed to authenticate with server ({})"), ssh_get_error(_session)));
 	}
 
 LIBDCP_DISABLE_WARNINGS
 	_scp = ssh_scp_new (_session, SSH_SCP_WRITE | SSH_SCP_RECURSIVE, Config::instance()->tms_path().c_str());
 LIBDCP_ENABLE_WARNINGS
 	if (!_scp) {
-		throw NetworkError (String::compose(_("SSH error [%1] (%2)"), "ssh_scp_new", ssh_get_error(_session)));
+		throw NetworkError(fmt::format(_("SSH error [{}] ({})"), "ssh_scp_new", ssh_get_error(_session)));
 	}
 
 LIBDCP_DISABLE_WARNINGS
 	r = ssh_scp_init (_scp);
 LIBDCP_ENABLE_WARNINGS
 	if (r != SSH_OK) {
-		throw NetworkError (String::compose(_("SSH error [%1] (%2)"), "ssh_scp_init", ssh_get_error(_session)));
+		throw NetworkError(fmt::format(_("SSH error [{}] ({})"), "ssh_scp_init", ssh_get_error(_session)));
 	}
 }
 
@@ -103,7 +102,7 @@ LIBDCP_DISABLE_WARNINGS
 	int const r = ssh_scp_push_directory (_scp, directory.generic_string().c_str(), S_IRWXU);
 LIBDCP_ENABLE_WARNINGS
 	if (r != SSH_OK) {
-		throw NetworkError (String::compose(_("Could not create remote directory %1 (%2)"), directory, ssh_get_error(_session)));
+		throw NetworkError(fmt::format(_("Could not create remote directory {} ({})"), directory.string(), ssh_get_error(_session)));
 	}
 }
 
@@ -119,7 +118,7 @@ LIBDCP_ENABLE_WARNINGS
 
 	dcp::File f(from, "rb");
 	if (!f) {
-		throw NetworkError (String::compose(_("Could not open %1 to send"), from));
+		throw NetworkError(fmt::format(_("Could not open {} to send"), from.string()));
 	}
 
 	boost::uintmax_t buffer_size = 64 * 1024;
@@ -136,7 +135,7 @@ LIBDCP_DISABLE_WARNINGS
 		int const r = ssh_scp_write (_scp, buffer, t);
 LIBDCP_ENABLE_WARNINGS
 		if (r != SSH_OK) {
-			throw NetworkError (String::compose(_("Could not write to remote file (%1)"), ssh_get_error(_session)));
+			throw NetworkError(fmt::format(_("Could not write to remote file ({})"), ssh_get_error(_session)));
 		}
 		to_do -= t;
 		transferred += t;
diff --git a/src/lib/send_kdm_email_job.cc b/src/lib/send_kdm_email_job.cc
index 59e33d4bc..e088de069 100644
--- a/src/lib/send_kdm_email_job.cc
+++ b/src/lib/send_kdm_email_job.cc
@@ -19,10 +19,10 @@
 */
 
 
-#include "compose.hpp"
 #include "film.h"
 #include "kdm_with_metadata.h"
 #include "send_kdm_email_job.h"
+#include <fmt/format.h>
 #include <list>
 
 #include "i18n.h"
@@ -94,7 +94,7 @@ SendKDMEmailJob::name () const
 		return _("Email KDMs");
 	}
 
-	return String::compose (_("Email KDMs for %1"), *f);
+	return fmt::format(_("Email KDMs for {}"), *f);
 }
 
 
diff --git a/src/lib/send_problem_report_job.cc b/src/lib/send_problem_report_job.cc
index ed78112e9..d3570c83f 100644
--- a/src/lib/send_problem_report_job.cc
+++ b/src/lib/send_problem_report_job.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "cross.h"
 #include "email.h"
 #include "environment_info.h"
@@ -29,6 +28,7 @@
 #include "send_problem_report_job.h"
 #include "variant.h"
 #include "version.h"
+#include <fmt/format.h>
 #include <libxml++/libxml++.h>
 
 #include "i18n.h"
@@ -69,7 +69,7 @@ SendProblemReportJob::name () const
 		return _("Email problem report");
 	}
 
-	return String::compose (_("Email problem report for %1"), _film->name());
+	return fmt::format(_("Email problem report for {}"), _film->name());
 }
 
 
@@ -109,7 +109,7 @@ SendProblemReportJob::run ()
 		body += "---<8----\n";
 	}
 
-	Email email(_from, {"carl@dcpomatic.com"}, variant::insert_dcpomatic("%1 problem report"), body);
+	Email email(_from, {"carl@dcpomatic.com"}, variant::insert_dcpomatic("{} problem report"), body);
 	email.send("main.carlh.net", 2525, EmailProtocol::STARTTLS);
 
 	set_progress (1);
diff --git a/src/lib/shuffler.cc b/src/lib/shuffler.cc
index a4ea0f5dc..6b477073c 100644
--- a/src/lib/shuffler.cc
+++ b/src/lib/shuffler.cc
@@ -23,6 +23,7 @@
 #include "content_video.h"
 #include "dcpomatic_assert.h"
 #include "dcpomatic_log.h"
+#include <fmt/format.h>
 #include <string>
 #include <iostream>
 
@@ -51,7 +52,7 @@ struct Comparator
 void
 Shuffler::video (weak_ptr<Piece> weak_piece, ContentVideo video)
 {
-	LOG_DEBUG_THREE_D("Shuffler::video time=%1 eyes=%2 part=%3", to_string(video.time), static_cast<int>(video.eyes), static_cast<int>(video.part));
+	LOG_DEBUG_THREE_D("Shuffler::video time={} eyes={} part={}", to_string(video.time), static_cast<int>(video.eyes), static_cast<int>(video.part));
 
 	if (video.eyes != Eyes::LEFT && video.eyes != Eyes::RIGHT) {
 		/* Pass through anything that we don't care about */
@@ -84,9 +85,9 @@ Shuffler::video (weak_ptr<Piece> weak_piece, ContentVideo video)
 				);
 
 		if (!store_front_in_sequence) {
-			string const store = _store.empty() ? "store empty" : String::compose("store front time=%1 eyes=%2", to_string(_store.front().second.time), static_cast<int>(_store.front().second.eyes));
-			string const last = _last ? String::compose("last time=%1 eyes=%2", to_string(_last->time), static_cast<int>(_last->eyes)) : "no last";
-			LOG_DEBUG_THREE_D("Shuffler not in sequence: %1 %2", store, last);
+			string const store = _store.empty() ? "store empty" : fmt::format("store front time={} eyes={}", to_string(_store.front().second.time), static_cast<int>(_store.front().second.eyes));
+			string const last = _last ? fmt::format("last time={} eyes={}", to_string(_last->time), static_cast<int>(_last->eyes)) : "no last";
+			LOG_DEBUG_THREE_D("Shuffler not in sequence: {} {}", store, last);
 		}
 
 		if (!store_front_in_sequence && _store.size() <= _max_size) {
@@ -98,10 +99,10 @@ Shuffler::video (weak_ptr<Piece> weak_piece, ContentVideo video)
 		}
 
 		if (_store.size() > _max_size) {
-			LOG_WARNING("Shuffler is full after receiving frame at %1; 3D sync may be incorrect.", to_string(video.time));
+			LOG_WARNING("Shuffler is full after receiving frame at {}; 3D sync may be incorrect.", to_string(video.time));
 		}
 
-		LOG_DEBUG_THREE_D("Shuffler emits time=%1 eyes=%2 store=%3", to_string(_store.front().second.time), static_cast<int>(_store.front().second.eyes), _store.size());
+		LOG_DEBUG_THREE_D("Shuffler emits time={} eyes={} store={}", to_string(_store.front().second.time), static_cast<int>(_store.front().second.eyes), _store.size());
 		Video (_store.front().first, _store.front().second);
 		_last = _store.front().second;
 		_store.pop_front ();
diff --git a/src/lib/sqlite_table.cc b/src/lib/sqlite_table.cc
index f00fa6b74..03c0278df 100644
--- a/src/lib/sqlite_table.cc
+++ b/src/lib/sqlite_table.cc
@@ -20,9 +20,9 @@
 
 
 #include "dcpomatic_assert.h"
-#include "compose.hpp"
 #include "sqlite_table.h"
 #include "util.h"
+#include <fmt/format.h>
 
 
 using std::string;
@@ -46,7 +46,7 @@ SQLiteTable::create() const
 	for (size_t i = 0; i < _columns.size(); ++i) {
 		columns[i] = _columns[i] + " " + _types[i];
 	}
-	return String::compose("CREATE TABLE IF NOT EXISTS %1 (id INTEGER PRIMARY KEY, %2)", _name, join_strings(columns, ", "));
+	return fmt::format("CREATE TABLE IF NOT EXISTS {} (id INTEGER PRIMARY KEY, {})", _name, join_strings(columns, ", "));
 }
 
 
@@ -55,7 +55,7 @@ SQLiteTable::insert() const
 {
 	DCPOMATIC_ASSERT(!_columns.empty());
 	vector<string> placeholders(_columns.size(), "?");
-	return String::compose("INSERT INTO %1 (%2) VALUES (%3)", _name, join_strings(_columns, ", "), join_strings(placeholders, ", "));
+	return fmt::format("INSERT INTO {} ({}) VALUES ({})", _name, join_strings(_columns, ", "), join_strings(placeholders, ", "));
 }
 
 
@@ -68,12 +68,12 @@ SQLiteTable::update(string const& condition) const
 		placeholders[i] = _columns[i] + "=?";
 	}
 
-	return String::compose("UPDATE %1 SET %2 %3", _name, join_strings(placeholders, ", "), condition);
+	return fmt::format("UPDATE {} SET {} {}", _name, join_strings(placeholders, ", "), condition);
 }
 
 
 string
 SQLiteTable::select(string const& condition) const
 {
-	return String::compose("SELECT id,%1 FROM %2 %3", join_strings(_columns, ","), _name, condition);
+	return fmt::format("SELECT id,{} FROM {} {}", join_strings(_columns, ","), _name, condition);
 }
diff --git a/src/lib/subtitle_film_encoder.cc b/src/lib/subtitle_film_encoder.cc
index 8dff4bc5c..fc9ce92ee 100644
--- a/src/lib/subtitle_film_encoder.cc
+++ b/src/lib/subtitle_film_encoder.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "film.h"
 #include "job.h"
 #include "player.h"
@@ -70,9 +69,9 @@ SubtitleFilmEncoder::SubtitleFilmEncoder(shared_ptr<const Film> film, shared_ptr
 		boost::filesystem::path filename = output;
 		if (dcp::filesystem::is_directory(filename)) {
 			if (files > 1) {
-				/// TRANSLATORS: _reel%1 here is to be added to an export filename to indicate
-				/// which reel it is.  Preserve the %1; it will be replaced with the reel number.
-				filename /= String::compose("%1_reel%2", initial_name, i + 1);
+				/// TRANSLATORS: _reel{} here is to be added to an export filename to indicate
+				/// which reel it is.  Preserve the {}; it will be replaced with the reel number.
+				filename /= fmt::format("{}_reel{}", initial_name, i + 1);
 			} else {
 				filename /= initial_name;
 			}
diff --git a/src/lib/text_content.cc b/src/lib/text_content.cc
index 15e1d4055..3c5eb5527 100644
--- a/src/lib/text_content.cc
+++ b/src/lib/text_content.cc
@@ -27,6 +27,7 @@
 #include "variant.h"
 #include <libcxml/cxml.h>
 #include <libxml++/libxml++.h>
+#include <fmt/format.h>
 #include <iostream>
 
 #include "i18n.h"
@@ -245,9 +246,9 @@ TextContent::TextContent (Content* parent, cxml::ConstNodePtr node, int version,
 			 */
 			if (version <= 37) {
 				if (!lang->content().empty()) {
-					notes.push_back(String::compose(
-						_("A subtitle or closed caption file in this project is marked with the language '%1', "
-						  "which %2 does not recognise.  The file's language has been cleared."), lang->content(), variant::dcpomatic()));
+					notes.push_back(fmt::format(
+						_("A subtitle or closed caption file in this project is marked with the language '{}', "
+						  "which {} does not recognise.  The file's language has been cleared."), lang->content(), variant::dcpomatic()));
 				}
 			} else {
 				throw;
diff --git a/src/lib/text_decoder.cc b/src/lib/text_decoder.cc
index db072eda6..33f3862d5 100644
--- a/src/lib/text_decoder.cc
+++ b/src/lib/text_decoder.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "dcpomatic_log.h"
 #include "log.h"
 #include "text_content.h"
@@ -308,7 +307,7 @@ TextDecoder::emit_plain_start (ContentTime from, sub::Subtitle const & sub_subti
 
 			auto font = content()->get_font(block.font.get_value_or(""));
 			if (!font) {
-				LOG_WARNING("Could not find font '%1' in content; falling back to default", block.font.get_value_or(""));
+				LOG_WARNING("Could not find font '{}' in content; falling back to default", block.font.get_value_or(""));
 				font = std::make_shared<dcpomatic::Font>(block.font.get_value_or(""), default_font_file());
 			}
 			DCPOMATIC_ASSERT(font);
diff --git a/src/lib/text_type.cc b/src/lib/text_type.cc
index 33e74bdca..fa0d9e146 100644
--- a/src/lib/text_type.cc
+++ b/src/lib/text_type.cc
@@ -19,12 +19,12 @@
 */
 
 
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
 #include "exceptions.h"
 #include "text_type.h"
 #include "types.h"
 #include <dcp/text_type.h>
+#include <fmt/format.h>
 
 #include "i18n.h"
 
@@ -46,7 +46,7 @@ string_to_text_type(string s)
 	} else if (s == "closed-caption") {
 		return TextType::CLOSED_CAPTION;
 	} else {
-		throw MetadataError(String::compose("Unknown text type %1", s));
+		throw MetadataError(fmt::format("Unknown text type {}", s));
 	}
 }
 
diff --git a/src/lib/timer.cc b/src/lib/timer.cc
index caef89e0e..0c823de2f 100644
--- a/src/lib/timer.cc
+++ b/src/lib/timer.cc
@@ -24,9 +24,9 @@
  */
 
 
-#include "compose.hpp"
 #include "timer.h"
 #include "util.h"
+#include <fmt/format.h>
 #include <sys/time.h>
 #include <iostream>
 
@@ -130,7 +130,7 @@ StateTimer::~StateTimer ()
 		char buffer[64];
 		snprintf (buffer, 64, "%.4f", i.second.total_time);
 		string total_time (buffer);
-		sorted.push_back (make_pair(i.second.total_time, String::compose("\t%1%2 %3 %4", name, total_time, i.second.number, (i.second.total_time / i.second.number))));
+		sorted.push_back(make_pair(i.second.total_time, fmt::format("\t{}{} {} {}", name, total_time, i.second.number, (i.second.total_time / i.second.number))));
 	}
 
 	sorted.sort ([](pair<double, string> const& a, pair<double, string> const& b) {
diff --git a/src/lib/transcode_job.cc b/src/lib/transcode_job.cc
index f1373fb4a..bdb0cb2b1 100644
--- a/src/lib/transcode_job.cc
+++ b/src/lib/transcode_job.cc
@@ -25,7 +25,6 @@
 
 
 #include "analytics.h"
-#include "compose.hpp"
 #include "content.h"
 #include "config.h"
 #include "dcp_film_encoder.h"
@@ -72,7 +71,7 @@ TranscodeJob::~TranscodeJob ()
 string
 TranscodeJob::name () const
 {
-	return String::compose (_("Transcoding %1"), _film->name());
+	return fmt::format(_("Transcoding {}"), _film->name());
 }
 
 
@@ -113,7 +112,7 @@ TranscodeJob::run ()
 				set_progress (1);
 				set_error(
 					_("Files have changed since they were added to the project."),
-					variant::insert_dcpomatic(_("Open the project in %1, check the settings, then save it before trying again."))
+					variant::insert_dcpomatic(_("Open the project in {}, check the settings, then save it before trying again."))
 					);
 				set_state (FINISHED_ERROR);
 				return;
@@ -131,13 +130,13 @@ TranscodeJob::run ()
 		set_progress (1);
 		set_state (FINISHED_OK);
 
-		LOG_GENERAL(N_("Transcode job completed successfully: %1 fps"), dcp::locale_convert<string>(frames_per_second(), 2, true));
+		LOG_GENERAL(N_("Transcode job completed successfully: {} fps"), dcp::locale_convert<string>(frames_per_second(), 2, true));
 
 		if (variant::count_created_dcps() && dynamic_pointer_cast<DCPFilmEncoder>(_encoder)) {
 			try {
 				Analytics::instance()->successful_dcp_encode();
 			} catch (FileError& e) {
-				LOG_WARNING (N_("Failed to write analytics (%1)"), e.what());
+				LOG_WARNING(N_("Failed to write analytics ({})"), e.what());
 			}
 		}
 
@@ -177,10 +176,10 @@ TranscodeJob::status () const
 		return Job::status();
 	}
 
-	auto status = String::compose(_("%1; %2/%3 frames"), Job::status(), _encoder->frames_done(), _film->length().frames_round(_film->video_frame_rate()));
+	auto status = fmt::format(_("{}; {}/{} frames"), Job::status(), _encoder->frames_done(), _film->length().frames_round(_film->video_frame_rate()));
 	if (auto const fps = _encoder->current_rate()) {
 		/// TRANSLATORS: fps here is an abbreviation for frames per second
-		status += String::compose(_("; %1 fps"), dcp::locale_convert<string>(*fps, 1, true));
+		status += fmt::format(_("; {} fps"), dcp::locale_convert<string>(*fps, 1, true));
 	}
 
 	return status;
diff --git a/src/lib/types.cc b/src/lib/types.cc
index 48363f892..2ef2bbf8c 100644
--- a/src/lib/types.cc
+++ b/src/lib/types.cc
@@ -18,9 +18,8 @@
 
 */
 
-#include "types.h"
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
+#include "types.h"
 #include <dcp/cpl.h>
 #include <dcp/dcp.h>
 #include <dcp/filesystem.h>
diff --git a/src/lib/unzipper.cc b/src/lib/unzipper.cc
index 8d468f24f..2f9510347 100644
--- a/src/lib/unzipper.cc
+++ b/src/lib/unzipper.cc
@@ -22,9 +22,11 @@
 #include "dcpomatic_assert.h"
 #include "exceptions.h"
 #include "unzipper.h"
+#include <dcp/array_data.h>
 #include <dcp/filesystem.h>
 #include <dcp/scope_guard.h>
 #include <zip.h>
+#include <fmt/format.h>
 #include <boost/filesystem.hpp>
 #include <stdexcept>
 
@@ -73,7 +75,7 @@ Unzipper::get(string const& filename) const
 {
 	auto file = zip_fopen(_zip, filename.c_str(), 0);
 	if (!file) {
-		throw runtime_error(String::compose(_("Could not find file %1 in ZIP file"), filename));
+		throw runtime_error(fmt::format(_("Could not find file {} in ZIP file"), filename));
 	}
 
 	dcp::ScopeGuard sg = [file]() { zip_fclose(file); };
diff --git a/src/lib/uploader.cc b/src/lib/uploader.cc
index f2a47f50e..bd5955602 100644
--- a/src/lib/uploader.cc
+++ b/src/lib/uploader.cc
@@ -21,13 +21,12 @@
 
 #include "uploader.h"
 #include "dcpomatic_assert.h"
-#include "compose.hpp"
+#include <fmt/format.h>
 
 #include "i18n.h"
 
 
 using std::string;
-using std::shared_ptr;
 using std::function;
 
 
@@ -76,7 +75,7 @@ Uploader::upload_directory (boost::filesystem::path base, boost::filesystem::pat
 		if (is_directory(i.path())) {
 			upload_directory (base, i.path(), transferred, total_size);
 		} else {
-			_set_status(String::compose(_("copying %1"), i.path().filename()));
+			_set_status(fmt::format(_("copying {}"), i.path().filename().string()));
 			upload_file (i.path(), remove_prefix (base, i.path()), transferred, total_size);
 		}
 	}
diff --git a/src/lib/util.cc b/src/lib/util.cc
index bc0b44dd4..01f126559 100644
--- a/src/lib/util.cc
+++ b/src/lib/util.cc
@@ -29,7 +29,6 @@
 #include "audio_buffers.h"
 #include "audio_processor.h"
 #include "cinema_sound_processor.h"
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "cross.h"
@@ -380,7 +379,7 @@ public:
 		if (entry.TestFilter(m_filter)) {
 			string buffer;
 			entry.CreateStringWithOptions(buffer, m_options);
-			LOG_GENERAL("asdcplib: %1", buffer);
+			LOG_GENERAL("asdcplib: {}", buffer);
 		}
 	}
 };
@@ -407,7 +406,7 @@ ffmpeg_log_callback(void* ptr, int level, const char* fmt, va_list vl)
 	av_log_format_line(ptr, level, fmt, vl, line, sizeof (line), &prefix);
 	string str(line);
 	boost::algorithm::trim(str);
-	dcpomatic_log->log(String::compose("FFmpeg: %1", str), LogEntry::TYPE_GENERAL);
+	dcpomatic_log->log(fmt::format("FFmpeg: {}", str), LogEntry::TYPE_GENERAL);
 }
 
 
@@ -458,7 +457,7 @@ LIBDCP_ENABLE_WARNINGS
 	putenv ("PANGOCAIRO_BACKEND=fontconfig");
 	if (dcp::filesystem::exists(resources_path() / "fonts.conf")) {
 		/* The actual application after installation */
-		putenv(String::compose("FONTCONFIG_PATH=%1", resources_path().string()).c_str());
+		putenv(fmt::format("FONTCONFIG_PATH={}", resources_path().string()).c_str());
 	} else {
 		/* The place where fonts.conf is during tests */
 		putenv("FONTCONFIG_PATH=build\\fonts");
@@ -538,11 +537,11 @@ dcpomatic_setup_gettext_i18n (string lang)
 		/* Override our environment language.  Note that the caller must not
 		   free the string passed into putenv().
 		*/
-		string s = String::compose ("LANGUAGE=%1", lang);
+		string s = fmt::format("LANGUAGE={}", lang);
 		putenv (strdup (s.c_str ()));
-		s = String::compose ("LANG=%1", lang);
+		s = fmt::format("LANG={}", lang);
 		putenv (strdup (s.c_str ()));
-		s = String::compose ("LC_ALL=%1", lang);
+		s = fmt::format("LC_ALL={}", lang);
 		putenv (strdup (s.c_str ()));
 	}
 
@@ -1029,9 +1028,9 @@ decrypt_kdm_with_helpful_error (dcp::EncryptedKDM kdm)
 			}
 		}
 		if (!on_chain) {
-			throw KDMError(variant::insert_dcpomatic(_("This KDM was not made for %1's decryption certificate.")), e.what());
+			throw KDMError(variant::insert_dcpomatic(_("This KDM was not made for {}'s decryption certificate.")), e.what());
 		} else if (kdm_subject_name != dc->leaf().subject()) {
-			throw KDMError(variant::insert_dcpomatic(_("This KDM was made for %1 but not for its leaf certificate.")), e.what());
+			throw KDMError(variant::insert_dcpomatic(_("This KDM was made for {} but not for its leaf certificate.")), e.what());
 		} else {
 			throw;
 		}
@@ -1089,7 +1088,7 @@ start_of_thread (string)
 string
 error_details(boost::system::error_code ec)
 {
-	return String::compose("%1:%2:%3", ec.category().name(), ec.value(), ec.message());
+	return fmt::format("{}:{}:{}", ec.category().name(), ec.value(), ec.message());
 }
 
 
@@ -1193,7 +1192,7 @@ screen_names_to_string(vector<string> names)
 string
 report_problem()
 {
-	return String::compose(_("Please report this problem by using Help -> Report a problem or via email to %1"), variant::report_problem_email());
+	return fmt::format(_("Please report this problem by using Help -> Report a problem or via email to {}"), variant::report_problem_email());
 }
 
 
diff --git a/src/lib/variant.cc b/src/lib/variant.cc
index a9dc56307..81931dcf7 100644
--- a/src/lib/variant.cc
+++ b/src/lib/variant.cc
@@ -20,6 +20,7 @@
 
 
 #include "variant.h"
+#include <fmt/format.h>
 
 
 static char const* _dcpomatic = "DCP-o-matic";
@@ -108,19 +109,19 @@ variant::dcpomatic_verifier()
 std::string
 variant::insert_dcpomatic(std::string const& s)
 {
-	return String::compose(s, _dcpomatic);
+	return fmt::format(s, _dcpomatic);
 }
 
 std::string
 variant::insert_dcpomatic_encode_server(std::string const& s)
 {
-	return String::compose(s, _dcpomatic_encode_server);
+	return fmt::format(s, _dcpomatic_encode_server);
 }
 
 std::string
 variant::insert_dcpomatic_kdm_creator(std::string const& s)
 {
-	return String::compose(s, _dcpomatic_kdm_creator);
+	return fmt::format(s, _dcpomatic_kdm_creator);
 }
 
 std::string
diff --git a/src/lib/variant.h b/src/lib/variant.h
index 9a42f3eca..c7e26c1d6 100644
--- a/src/lib/variant.h
+++ b/src/lib/variant.h
@@ -19,7 +19,7 @@
 */
 
 
-#include "compose.hpp"
+#include <string>
 
 
 namespace variant
diff --git a/src/lib/video_content.cc b/src/lib/video_content.cc
index dc658144a..7fa39c89d 100644
--- a/src/lib/video_content.cc
+++ b/src/lib/video_content.cc
@@ -20,7 +20,6 @@
 
 
 #include "colour_conversion.h"
-#include "compose.hpp"
 #include "config.h"
 #include "content.h"
 #include "dcpomatic_log.h"
@@ -332,7 +331,7 @@ VideoContent::take_from_examiner(shared_ptr<const Film> film, shared_ptr<VideoEx
 		_pixel_quanta = pixel_quanta;
 	}
 
-	LOG_GENERAL ("Video length obtained from header as %1 frames", _length);
+	LOG_GENERAL ("Video length obtained from header as {} frames", _length);
 
 	if (d->video_frame_rate()) {
 		_parent->set_video_frame_rate(film, d->video_frame_rate().get());
@@ -372,16 +371,16 @@ VideoContent::identifier () const
 string
 VideoContent::technical_summary () const
 {
-	string const size_string = size() ? String::compose("%1x%2", size()->width, size()->height) : _("unknown");
+	string const size_string = size() ? fmt::format("{}x{}", size()->width, size()->height) : _("unknown");
 
-	string s = String::compose (
-		N_("video: length %1 frames, size %2"),
+	string s = fmt::format(
+		N_("video: length {} frames, size {}"),
 		length_after_3d_combine(),
 		size_string
 		);
 
 	if (sample_aspect_ratio ()) {
-		s += String::compose (N_(", sample aspect ratio %1"), (sample_aspect_ratio().get ()));
+		s += fmt::format(N_(", sample aspect ratio {}"), (sample_aspect_ratio().get ()));
 	}
 
 	return s;
@@ -456,8 +455,8 @@ VideoContent::processing_description (shared_ptr<const Film> film)
 	char buffer[256];
 
 	if (size() && size()->width && size()->height) {
-		d += String::compose (
-			_("Content video is %1x%2"),
+		d += fmt::format(
+			_("Content video is {}x{}"),
 			size_after_3d_split()->width,
 			size_after_3d_split()->height
 			);
@@ -480,8 +479,8 @@ VideoContent::processing_description (shared_ptr<const Film> film)
 	if ((crop.left || crop.right || crop.top || crop.bottom) && size() != dcp::Size(0, 0)) {
 		auto const cropped = size_after_crop ();
 		if (cropped) {
-			d += String::compose (
-				_("\nCropped to %1x%2"),
+			d += fmt::format(
+				_("\nCropped to {}x{}"),
 				cropped->width, cropped->height
 				);
 
@@ -494,8 +493,8 @@ VideoContent::processing_description (shared_ptr<const Film> film)
 	auto const scaled = scaled_size (container_size);
 
 	if (scaled && *scaled != size_after_crop()) {
-		d += String::compose (
-			_("\nScaled to %1x%2"),
+		d += fmt::format(
+			_("\nScaled to {}x{}"),
 			scaled->width, scaled->height
 			);
 
@@ -504,8 +503,8 @@ VideoContent::processing_description (shared_ptr<const Film> film)
 	}
 
 	if (scaled && *scaled != container_size) {
-		d += String::compose (
-			_("\nPadded with black to fit container %1 (%2x%3)"),
+		d += fmt::format(
+			_("\nPadded with black to fit container {} ({}x{})"),
 			film->container()->container_nickname (),
 			container_size.width, container_size.height
 			);
@@ -532,7 +531,7 @@ VideoContent::add_properties (list<UserProperty>& p) const
 {
 	p.push_back (UserProperty (UserProperty::VIDEO, _("Length"), length (), _("video frames")));
 	if (auto s = size()) {
-		p.push_back(UserProperty(UserProperty::VIDEO, _("Size"), String::compose("%1x%2", s->width, s->height)));
+		p.push_back(UserProperty(UserProperty::VIDEO, _("Size"), fmt::format("{}x{}", s->width, s->height)));
 	}
 }
 
diff --git a/src/lib/video_decoder.cc b/src/lib/video_decoder.cc
index c628fddd9..15c9fd8fd 100644
--- a/src/lib/video_decoder.cc
+++ b/src/lib/video_decoder.cc
@@ -19,13 +19,13 @@
 */
 
 
-#include "compose.hpp"
 #include "frame_interval_checker.h"
 #include "image.h"
 #include "j2k_image_proxy.h"
 #include "log.h"
 #include "raw_image_proxy.h"
 #include "video_decoder.h"
+#include <fmt/format.h>
 #include <iostream>
 
 #include "i18n.h"
@@ -66,10 +66,10 @@ VideoDecoder::emit(shared_ptr<const Film> film, shared_ptr<const ImageProxy> ima
 		if (_frame_interval_checker->guess() == FrameIntervalChecker::PROBABLY_NOT_3D && vft == VideoFrameType::THREE_D) {
 			boost::throw_exception (
 				DecodeError(
-					String::compose(
-						_("The content file %1 is set as 3D but does not appear to contain 3D images.  Please set it to 2D.  "
+					fmt::format(
+						_("The content file {} is set as 3D but does not appear to contain 3D images.  Please set it to 2D.  "
 						  "You can still make a 3D DCP from this content by ticking the 3D option in the DCP video tab."),
-						_content->path(0)
+						_content->path(0).string()
 						)
 					)
 				);
diff --git a/src/lib/video_filter_graph.cc b/src/lib/video_filter_graph.cc
index d5840c6d3..e78850908 100644
--- a/src/lib/video_filter_graph.cc
+++ b/src/lib/video_filter_graph.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
 #include "exceptions.h"
 #include "image.h"
@@ -76,7 +75,7 @@ VideoFilterGraph::process(shared_ptr<const Image> image)
 
 	int r = av_buffersrc_write_frame(_buffer_src_context, frame);
 	if (r < 0) {
-		throw DecodeError(String::compose(N_("could not push buffer into filter chain (%1)."), r));
+		throw DecodeError(fmt::format(N_("could not push buffer into filter chain ({})."), r));
 	}
 
 	list<shared_ptr<const Image>> images;
@@ -107,7 +106,7 @@ VideoFilterGraph::process (AVFrame* frame)
 	} else {
 		int r = av_buffersrc_write_frame (_buffer_src_context, frame);
 		if (r < 0) {
-			throw DecodeError (String::compose(N_("could not push buffer into filter chain (%1)."), r));
+			throw DecodeError(fmt::format(N_("could not push buffer into filter chain ({})."), r));
 		}
 
 		while (true) {
diff --git a/src/lib/video_filter_graph_set.cc b/src/lib/video_filter_graph_set.cc
index dbae17d4c..0c966d3ac 100644
--- a/src/lib/video_filter_graph_set.cc
+++ b/src/lib/video_filter_graph_set.cc
@@ -48,7 +48,7 @@ VideoFilterGraphSet::get(dcp::Size size, AVPixelFormat format)
 	new_graph->setup(_filters);
 	_graphs.push_back(new_graph);
 
-	LOG_GENERAL(N_("New graph for %1x%2, pixel format %3"), size.width, size.height, static_cast<int>(format));
+	LOG_GENERAL(N_("New graph for {}x{}, pixel format {}"), size.width, size.height, static_cast<int>(format));
 
 	return new_graph;
 }
diff --git a/src/lib/video_mxf_content.cc b/src/lib/video_mxf_content.cc
index ded81e6bf..533a12bb0 100644
--- a/src/lib/video_mxf_content.cc
+++ b/src/lib/video_mxf_content.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "film.h"
 #include "job.h"
 #include "video_content.h"
@@ -30,6 +29,7 @@
 #include <dcp/mono_j2k_picture_asset.h>
 #include <dcp/stereo_j2k_picture_asset.h>
 #include <libxml++/libxml++.h>
+#include <fmt/format.h>
 
 #include "i18n.h"
 
@@ -103,7 +103,7 @@ VideoMXFContent::examine (shared_ptr<const Film> film, shared_ptr<Job> job)
 string
 VideoMXFContent::summary () const
 {
-	return String::compose (_("%1 [video]"), path_summary());
+	return fmt::format(_("{} [video]"), path_summary());
 }
 
 
diff --git a/src/lib/video_ring_buffers.cc b/src/lib/video_ring_buffers.cc
index 63c52ee06..00df2f9cc 100644
--- a/src/lib/video_ring_buffers.cc
+++ b/src/lib/video_ring_buffers.cc
@@ -21,17 +21,17 @@
 
 #include "video_ring_buffers.h"
 #include "player_video.h"
-#include "compose.hpp"
+#include <fmt/format.h>
 #include <list>
 #include <iostream>
 
 
+using std::cout;
 using std::list;
 using std::make_pair;
-using std::cout;
 using std::pair;
-using std::string;
 using std::shared_ptr;
+using std::string;
 using boost::optional;
 using namespace dcpomatic;
 
@@ -89,7 +89,7 @@ VideoRingBuffers::memory_used () const
 	for (auto const& i: _data) {
 		m += i.first->memory_used();
 	}
-	return make_pair(m, String::compose("%1 frames", _data.size()));
+	return make_pair(m, fmt::format("{} frames", _data.size()));
 }
 
 
diff --git a/src/lib/writer.cc b/src/lib/writer.cc
index 58a01badb..61785f558 100644
--- a/src/lib/writer.cc
+++ b/src/lib/writer.cc
@@ -21,7 +21,6 @@
 
 #include "audio_buffers.h"
 #include "audio_mapping.h"
-#include "compose.hpp"
 #include "config.h"
 #include "constants.h"
 #include "cross.h"
@@ -397,9 +396,9 @@ try
 			}
 
 			/* Nothing to do: wait until something happens which may indicate that we do */
-			LOG_TIMING (N_("writer-sleep queue=%1"), _queue.size());
+			LOG_TIMING(N_("writer-sleep queue={}"), _queue.size());
 			_empty_condition.wait (lock);
-			LOG_TIMING (N_("writer-wake queue=%1"), _queue.size());
+			LOG_TIMING(N_("writer-wake queue={}"), _queue.size());
 		}
 
 		/* We stop here if we have been asked to finish, and if either the queue
@@ -410,12 +409,12 @@ try
 		if (_finish && (!have_sequenced_image_at_queue_head() || _queue.empty())) {
 			/* (Hopefully temporarily) log anything that was not written */
 			if (!_queue.empty() && !have_sequenced_image_at_queue_head()) {
-				LOG_WARNING (N_("Finishing writer with a left-over queue of %1:"), _queue.size());
+				LOG_WARNING(N_("Finishing writer with a left-over queue of {}:"), _queue.size());
 				for (auto const& i: _queue) {
 					if (i.type == QueueItem::Type::FULL) {
-						LOG_WARNING (N_("- type FULL, frame %1, eyes %2"), i.frame, (int) i.eyes);
+						LOG_WARNING(N_("- type FULL, frame {}, eyes {}"), i.frame, (int) i.eyes);
 					} else {
-						LOG_WARNING (N_("- type FAKE, size %1, frame %2, eyes %3"), i.info.size, i.frame, (int) i.eyes);
+						LOG_WARNING(N_("- type FAKE, size {}, frame {}, eyes {}"), i.info.size, i.frame, (int) i.eyes);
 					}
 				}
 			}
@@ -437,7 +436,7 @@ try
 
 			switch (qi.type) {
 			case QueueItem::Type::FULL:
-				LOG_DEBUG_ENCODE (N_("Writer FULL-writes %1 (%2)"), qi.frame, (int) qi.eyes);
+				LOG_DEBUG_ENCODE(N_("Writer FULL-writes {} ({})"), qi.frame, (int) qi.eyes);
 				if (!qi.encoded) {
 					qi.encoded.reset (new ArrayData(film()->j2c_path(qi.reel, qi.frame, qi.eyes, false)));
 				}
@@ -445,12 +444,12 @@ try
 				++_full_written;
 				break;
 			case QueueItem::Type::FAKE:
-				LOG_DEBUG_ENCODE (N_("Writer FAKE-writes %1"), qi.frame);
+				LOG_DEBUG_ENCODE(N_("Writer FAKE-writes {}"), qi.frame);
 				reel.fake_write(qi.info);
 				++_fake_written;
 				break;
 			case QueueItem::Type::REPEAT:
-				LOG_DEBUG_ENCODE (N_("Writer REPEAT-writes %1"), qi.frame);
+				LOG_DEBUG_ENCODE(N_("Writer REPEAT-writes {}"), qi.frame);
 				reel.repeat_write (qi.frame, qi.eyes);
 				++_repeat_written;
 				break;
@@ -483,7 +482,7 @@ try
 			   thread could erase the last item in the list.
 			*/
 
-			LOG_GENERAL("Writer full; pushes %1 to disk while awaiting %2", item->frame, awaiting);
+			LOG_GENERAL("Writer full; pushes {} to disk while awaiting {}", item->frame, awaiting);
 
 			item->encoded->write_via_temp(
 				film()->j2c_path(item->reel, item->frame, item->eyes, true),
@@ -626,12 +625,12 @@ Writer::finish()
 
 	auto creator = Config::instance()->dcp_creator();
 	if (creator.empty()) {
-		creator = String::compose("DCP-o-matic %1 %2", dcpomatic_version, dcpomatic_git_commit);
+		creator = fmt::format("DCP-o-matic {} {}", dcpomatic_version, dcpomatic_git_commit);
 	}
 
 	auto issuer = Config::instance()->dcp_issuer();
 	if (issuer.empty()) {
-		issuer = String::compose("DCP-o-matic %1 %2", dcpomatic_version, dcpomatic_git_commit);
+		issuer = fmt::format("DCP-o-matic {} {}", dcpomatic_version, dcpomatic_git_commit);
 	}
 
 	cpl->set_creator (creator);
@@ -718,7 +717,7 @@ Writer::finish()
 	dcp.write_xml(signer, !film()->limit_to_smpte_bv20(), Config::instance()->dcp_metadata_filename_format());
 
 	LOG_GENERAL (
-		N_("Wrote %1 FULL, %2 FAKE, %3 REPEAT, %4 pushed to disk"), _full_written, _fake_written, _repeat_written, _pushed_to_disk
+		N_("Wrote {} FULL, {} FAKE, {} REPEAT, {} pushed to disk"), _full_written, _fake_written, _repeat_written, _pushed_to_disk
 		);
 
 	write_cover_sheet();
@@ -768,13 +767,13 @@ Writer::write_cover_sheet()
 	}
 
 	if (size > (1000000000L)) {
-		boost::algorithm::replace_all (text, "$SIZE", String::compose("%1GB", dcp::locale_convert<string>(size / 1000000000.0, 1, true)));
+		boost::algorithm::replace_all(text, "$SIZE", fmt::format("{}GB", dcp::locale_convert<string>(size / 1000000000.0, 1, true)));
 	} else {
-		boost::algorithm::replace_all (text, "$SIZE", String::compose("%1MB", dcp::locale_convert<string>(size / 1000000.0, 1, true)));
+		boost::algorithm::replace_all(text, "$SIZE", fmt::format("{}MB", dcp::locale_convert<string>(size / 1000000.0, 1, true)));
 	}
 
 	auto ch = audio_channel_types (film()->mapped_audio_channels(), film()->audio_channels());
-	auto description = String::compose("%1.%2", ch.first, ch.second);
+	auto description = fmt::format("{}.{}", ch.first, ch.second);
 
 	if (description == "0.0") {
 		description = _("None");
@@ -788,11 +787,11 @@ Writer::write_cover_sheet()
 	auto const hmsf = film()->length().split(film()->video_frame_rate());
 	string length;
 	if (hmsf.h == 0 && hmsf.m == 0) {
-		length = String::compose("%1s", hmsf.s);
+		length = fmt::format("{}s", hmsf.s);
 	} else if (hmsf.h == 0 && hmsf.m > 0) {
-		length = String::compose("%1m%2s", hmsf.m, hmsf.s);
+		length = fmt::format("{}m{}s", hmsf.m, hmsf.s);
 	} else if (hmsf.h > 0 && hmsf.m > 0) {
-		length = String::compose("%1h%2m%3s", hmsf.h, hmsf.m, hmsf.s);
+		length = fmt::format("{}h{}m{}s", hmsf.h, hmsf.m, hmsf.s);
 	}
 
 	boost::algorithm::replace_all (text, "$LENGTH", length);
diff --git a/src/lib/zipper.cc b/src/lib/zipper.cc
index 625f3049a..52f4b5615 100644
--- a/src/lib/zipper.cc
+++ b/src/lib/zipper.cc
@@ -24,6 +24,7 @@
 #include "zipper.h"
 #include <dcp/filesystem.h>
 #include <zip.h>
+#include <fmt/format.h>
 #include <boost/filesystem.hpp>
 #include <stdexcept>
 
@@ -62,7 +63,7 @@ Zipper::add (string name, string content)
 #else
 	if (zip_add(_zip, name.c_str(), source) == -1) {
 #endif
-		throw runtime_error(String::compose("failed to add data to ZIP archive (%1)", zip_strerror(_zip)));
+		throw runtime_error(fmt::format("failed to add data to ZIP archive ({})", zip_strerror(_zip)));
 	}
 }
 
diff --git a/src/tools/dcpomatic.cc b/src/tools/dcpomatic.cc
index 3d9d571af..c673a2099 100644
--- a/src/tools/dcpomatic.cc
+++ b/src/tools/dcpomatic.cc
@@ -61,7 +61,6 @@
 #include "lib/audio_content.h"
 #include "lib/check_content_job.h"
 #include "lib/cinema.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/constants.h"
 #include "lib/content.h"
@@ -1481,7 +1480,7 @@ private:
 		for (size_t i = 0; i < history.size(); ++i) {
 			string s;
 			if (i < 9) {
-				s = String::compose ("&%1 %2", i + 1, history[i].string());
+				s = fmt::format("&{} {}", i + 1, history[i].string());
 			} else {
 				s = history[i].string();
 			}
@@ -1648,7 +1647,7 @@ private:
 			setvbuf(hf_in, NULL, _IONBF, 128);
 			*stdin = *hf_in;
 
-			cout << variant::insert_dcpomatic("%1 is starting.") << "\n";
+			cout << variant::insert_dcpomatic("{} is starting.") << "\n";
 		}
 #endif
 			wxInitAllImageHandlers ();
@@ -1725,7 +1724,7 @@ private:
 				try {
 					_frame->load_film (_film_to_load);
 				} catch (exception& e) {
-					error_dialog (nullptr, std_to_wx(String::compose(wx_to_std(_("Could not load film %1 (%2)")), _film_to_load)), std_to_wx(e.what()));
+					error_dialog(nullptr, std_to_wx(fmt::format(wx_to_std(_("Could not load film {} ({})")), _film_to_load)), std_to_wx(e.what()));
 				}
 			}
 
diff --git a/src/tools/dcpomatic_batch.cc b/src/tools/dcpomatic_batch.cc
index 379a3c074..69e1dac1e 100644
--- a/src/tools/dcpomatic_batch.cc
+++ b/src/tools/dcpomatic_batch.cc
@@ -29,7 +29,6 @@
 #include "wx/wx_signal_manager.h"
 #include "wx/wx_util.h"
 #include "wx/wx_variant.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/dcpomatic_socket.h"
 #include "lib/film.h"
@@ -53,6 +52,7 @@ LIBDCP_DISABLE_WARNINGS
 #include <wx/stdpaths.h>
 #include <wx/wx.h>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 #include <iostream>
 #include <set>
 
@@ -493,7 +493,7 @@ class App : public wxApp
 				} catch (exception& e) {
 					error_dialog (
 						0,
-						std_to_wx(String::compose(wx_to_std(_("Could not load film %1")), i.string())),
+						std_to_wx(fmt::format(wx_to_std(_("Could not load film {}")), i.string())),
 						std_to_wx(e.what())
 						);
 				}
diff --git a/src/tools/dcpomatic_cli.cc b/src/tools/dcpomatic_cli.cc
index 7ee61ac23..908bcdc8b 100644
--- a/src/tools/dcpomatic_cli.cc
+++ b/src/tools/dcpomatic_cli.cc
@@ -67,7 +67,7 @@ static void
 help (string n)
 {
 	cerr << "Syntax: " << n << " [OPTION] [<FILM>]\n"
-	     << variant::insert_dcpomatic("  -v, --version                     show %1 version\n")
+	     << variant::insert_dcpomatic("  -v, --version                     show {} version\n")
 	     << "  -h, --help                        show this help\n"
 	     << "  -f, --flags                       show flags passed to C++ compiler on build\n"
 	     << "  -n, --no-progress                 do not print progress to stdout\n"
@@ -76,7 +76,7 @@ help (string n)
 	     << "  -j, --json <port>                 run a JSON server on the specified port\n"
 	     << "  -k, --keep-going                  keep running even when the job is complete\n"
 	     << "  -s, --servers <file>              specify servers to use in a text file\n"
-	     << variant::insert_dcpomatic("  -l, --list-servers                just display a list of encoding servers that %1 is configured to use; don't encode\n")
+	     << variant::insert_dcpomatic("  -l, --list-servers                just display a list of encoding servers that {} is configured to use; don't encode\n")
 	     << "  -d, --dcp-path                    echo DCP's path to stdout on successful completion (implies -n)\n"
 	     << "  -c, --config <dir>                directory containing config.xml and cinemas.xml\n"
 	     << "      --dump                        just dump a summary of the film's settings; don't encode\n"
diff --git a/src/tools/dcpomatic_combiner.cc b/src/tools/dcpomatic_combiner.cc
index 890f01ad0..1125876a3 100644
--- a/src/tools/dcpomatic_combiner.cc
+++ b/src/tools/dcpomatic_combiner.cc
@@ -36,6 +36,7 @@ LIBDCP_DISABLE_WARNINGS
 #include <wx/filepicker.h>
 LIBDCP_ENABLE_WARNINGS
 #include <wx/wx.h>
+#include <fmt/format.h>
 #include <boost/bind/bind.hpp>
 #include <boost/filesystem.hpp>
 #include <exception>
@@ -161,8 +162,8 @@ private:
 			if (!confirm_dialog (
 				    this,
 				    std_to_wx (
-					    String::compose(wx_to_std(_("The directory %1 already exists and is not empty.  "
-									"Are you sure you want to use it?")),
+					    fmt::format(wx_to_std(_("The directory {} already exists and is not empty.  "
+								    "Are you sure you want to use it?")),
 							    output.string())
 					    )
 				    )) {
diff --git a/src/tools/dcpomatic_disk.cc b/src/tools/dcpomatic_disk.cc
index b47addce9..55327040e 100644
--- a/src/tools/dcpomatic_disk.cc
+++ b/src/tools/dcpomatic_disk.cc
@@ -45,6 +45,7 @@
 #include <wx/cmdline.h>
 #include <wx/progdlg.h>
 #include <wx/wx.h>
+#include <fmt/format.h>
 LIBDCP_DISABLE_WARNINGS
 #include <boost/process.hpp>
 LIBDCP_ENABLE_WARNINGS
@@ -180,7 +181,7 @@ public:
 		 */
 		dcpomatic_log = make_shared<FileLog>(State::write_path("disk.log"));
 		dcpomatic_log->set_types (dcpomatic_log->types() | LogEntry::TYPE_DISK);
-		LOG_DISK("dcpomatic_disk %1 started", dcpomatic_git_commit);
+		LOG_DISK("dcpomatic_disk {} started", dcpomatic_git_commit);
 
 		{
 			int constexpr seconds_to_look = 3;
@@ -201,7 +202,7 @@ public:
 
 #ifdef DCPOMATIC_WINDOWS
 		/* We must use ::shell here, it seems, to avoid error code 740 (related to privilege escalation) */
-		LOG_DISK("Starting writer process %1", disk_writer_path().string());
+		LOG_DISK("Starting writer process {}", disk_writer_path().string());
 		_writer = new boost::process::child (disk_writer_path(), boost::process::shell, boost::process::windows::hide);
 #endif
 
@@ -209,7 +210,7 @@ public:
 		if (getenv("DCPOMATIC_NO_START_WRITER")) {
 			LOG_DISK_NC("Not starting writer process as DCPOMATIC_NO_START_WRITER is set");
 		} else {
-			LOG_DISK("Starting writer process %1", disk_writer_path().string());
+			LOG_DISK("Starting writer process {}", disk_writer_path().string());
 			_writer = new boost::process::child (disk_writer_path());
 		}
 #endif
@@ -251,7 +252,7 @@ private:
 #ifdef DCPOMATIC_OSX
 	void uninstall()
 	{
-		system(String::compose("osascript \"%1/uninstall_disk.applescript\"", resources_path().string()).c_str());
+		system(fmt::format("osascript \"{}/uninstall_disk.applescript\"", resources_path().string()).c_str());
 	}
 #endif
 
@@ -302,12 +303,12 @@ private:
 				if (reply && reply->type() == DiskWriterBackEndResponse::Type::PONG) {
 					return true;
 				} else if (reply) {
-					LOG_DISK("Unexpected response %1 to ping received (attempt %2)", static_cast<int>(reply->type()), attempt);
+					LOG_DISK("Unexpected response {} to ping received (attempt {})", static_cast<int>(reply->type()), attempt);
 				} else {
-					LOG_DISK("No reply received from ping (attempt %1)", attempt);
+					LOG_DISK("No reply received from ping (attempt {})", attempt);
 				}
 			} else {
-				LOG_DISK("Could not send ping to writer (attempt %1)", attempt);
+				LOG_DISK("Could not send ping to writer (attempt {})", attempt);
 			}
 			dcpomatic_sleep_seconds (1);
 			return false;
@@ -352,7 +353,7 @@ private:
 				return;
 			}
 
-			LOG_DISK("Sending unmount request to disk writer for %1", drive.as_xml());
+			LOG_DISK("Sending unmount request to disk writer for {}", drive.as_xml());
 			if (!_nanomsg.send(DISK_WRITER_UNMOUNT "\n", 2000)) {
 				LOG_DISK_NC("Failed to send unmount request.");
 				throw CommunicationFailedError ();
diff --git a/src/tools/dcpomatic_kdm.cc b/src/tools/dcpomatic_kdm.cc
index 64c7ca7e3..3ec2ff923 100644
--- a/src/tools/dcpomatic_kdm.cc
+++ b/src/tools/dcpomatic_kdm.cc
@@ -40,7 +40,6 @@
 #include "wx/wx_variant.h"
 #include "lib/cinema.h"
 #include "lib/collator.h"
-#include "lib/compose.hpp"
 #include "lib/constants.h"
 #include "lib/config.h"
 #include "lib/cross.h"
@@ -128,7 +127,7 @@ public:
 			setvbuf(hf_in, NULL, _IONBF, 128);
 			*stdin = *hf_in;
 
-			std::cout << variant::insert_dcpomatic_kdm_creator("%1 is starting.\n");
+			std::cout << variant::insert_dcpomatic_kdm_creator("{} is starting.\n");
 		}
 #endif
 
diff --git a/src/tools/dcpomatic_player.cc b/src/tools/dcpomatic_player.cc
index ed72de172..1893b43f6 100644
--- a/src/tools/dcpomatic_player.cc
+++ b/src/tools/dcpomatic_player.cc
@@ -38,7 +38,6 @@
 #include "wx/wx_signal_manager.h"
 #include "wx/wx_util.h"
 #include "wx/wx_variant.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/constants.h"
 #include "lib/cross.h"
@@ -74,7 +73,6 @@
 #include <dcp/dcp.h>
 #include <dcp/exceptions.h>
 #include <dcp/filesystem.h>
-#include <dcp/raw_convert.h>
 #include <dcp/scope_guard.h>
 #include <dcp/search.h>
 #include <dcp/warnings.h>
@@ -119,7 +117,6 @@ using boost::thread;
 #if BOOST_VERSION >= 106100
 using namespace boost::placeholders;
 #endif
-using dcp::raw_convert;
 using namespace dcpomatic;
 
 
@@ -914,17 +911,17 @@ private:
 			_viewer.panel()->Reparent(_dual_screen);
 			_viewer.panel()->SetFocus();
 			_dual_screen->Show ();
-			LOG_DEBUG_PLAYER("Setting up dual screen mode with %1 displays", wxDisplay::GetCount());
+			LOG_DEBUG_PLAYER("Setting up dual screen mode with {} displays", wxDisplay::GetCount());
 			for (auto index = 0U; index < wxDisplay::GetCount(); ++index) {
 				wxDisplay display(index);
 				auto client = display.GetClientArea();
 				auto mode = display.GetCurrentMode();
 				auto geometry = display.GetGeometry();
-				LOG_DEBUG_PLAYER("Display %1", index);
-				LOG_DEBUG_PLAYER("  ClientArea position=(%1, %2) size=(%3, %4)", client.GetX(), client.GetY(), client.GetWidth(), client.GetHeight());
-				LOG_DEBUG_PLAYER("  Geometry   position=(%1, %2) size=(%3, %4)", geometry.GetX(), geometry.GetY(), geometry.GetWidth(), geometry.GetHeight());
-				LOG_DEBUG_PLAYER("  Mode       size=(%1, %2)", mode.GetWidth(), mode.GetHeight());
-				LOG_DEBUG_PLAYER("  Primary?   %1", static_cast<int>(display.IsPrimary()));
+				LOG_DEBUG_PLAYER("Display {}", index);
+				LOG_DEBUG_PLAYER("  ClientArea position=({}, {}) size=({}, {})", client.GetX(), client.GetY(), client.GetWidth(), client.GetHeight());
+				LOG_DEBUG_PLAYER("  Geometry   position=({}, {}) size=({}, {})", geometry.GetX(), geometry.GetY(), geometry.GetWidth(), geometry.GetHeight());
+				LOG_DEBUG_PLAYER("  Mode       size=({}, {})", mode.GetWidth(), mode.GetHeight());
+				LOG_DEBUG_PLAYER("  Primary?   {}", static_cast<int>(display.IsPrimary()));
 			}
 			if (wxDisplay::GetCount() > 1) {
 				wxRect geometry[2] = {
@@ -1091,7 +1088,7 @@ private:
 				_http_server_thread = boost::thread(boost::bind(&HTTPServer::run, _http_server.get()));
 			}
 		} catch (std::exception& e) {
-			LOG_DEBUG_PLAYER("Failed to start player HTTP server (%1)", e.what());
+			LOG_DEBUG_PLAYER("Failed to start player HTTP server ({})", e.what());
 		}
 	}
 
@@ -1105,7 +1102,7 @@ private:
 			/* This is not the end of the world; probably a failure to bind the server socket
 			 * because there's already another player running.
 			 */
-			LOG_DEBUG_PLAYER("Failed to start internal player server (%1)", e.what());
+			LOG_DEBUG_PLAYER("Failed to start internal player server ({})", e.what());
 		}
 	}
 
@@ -1134,7 +1131,7 @@ private:
 		for (size_t i = 0; i < history.size(); ++i) {
 			string s;
 			if (i < 9) {
-				s = String::compose ("&%1 %2", i + 1, history[i].string());
+				s = fmt::format("&{} {}", i + 1, history[i].string());
 			} else {
 				s = history[i].string();
 			}
diff --git a/src/tools/dcpomatic_server.cc b/src/tools/dcpomatic_server.cc
index 5747e89af..b4c642a69 100644
--- a/src/tools/dcpomatic_server.cc
+++ b/src/tools/dcpomatic_server.cc
@@ -42,6 +42,7 @@ LIBDCP_DISABLE_WARNINGS
 #include <wx/splash.h>
 #include <wx/taskbar.h>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 #include <boost/thread.hpp>
 #include <boost/optional.hpp>
 #include <iostream>
@@ -250,7 +251,7 @@ public:
 #else
 		string const colour = gui_is_dark() ? "white" : "black";
 		wxBitmap bitmap (
-			bitmap_path(String::compose("dcpomatic_small_%1.png", colour)),
+			bitmap_path(fmt::format("dcpomatic_small_{}.png", colour)),
 			wxBITMAP_TYPE_PNG
 			);
 		wxIcon icon;
diff --git a/src/tools/dcpomatic_server_cli.cc b/src/tools/dcpomatic_server_cli.cc
index ea78d41a5..a20b14f68 100644
--- a/src/tools/dcpomatic_server_cli.cc
+++ b/src/tools/dcpomatic_server_cli.cc
@@ -56,7 +56,7 @@ static void
 help (string n)
 {
 	cerr << "Syntax: " << n << " [OPTION]\n"
-	     << variant::insert_dcpomatic("  -v, --version      show %1 version\n")
+	     << variant::insert_dcpomatic("  -v, --version      show {} version\n")
 	     << "  -h, --help         show this help\n"
 	     << "  -t, --threads      number of parallel encoding threads to use\n"
 	     << "  --verbose          be verbose to stdout\n"
@@ -127,7 +127,7 @@ main (int argc, char* argv[])
 		server.run ();
 	} catch (boost::system::system_error& e) {
 		if (e.code() == boost::system::errc::address_in_use) {
-			cerr << program_name << variant::insert_dcpomatic(": address already in use.  Is another %1 server instance already running?\n");
+			cerr << program_name << variant::insert_dcpomatic(": address already in use.  Is another {} server instance already running?\n");
 			exit (EXIT_FAILURE);
 		}
 		cerr << program_name << ": " << e.what() << "\n";
diff --git a/src/wx/about_dialog.cc b/src/wx/about_dialog.cc
index 345ae2582..258a87df0 100644
--- a/src/wx/about_dialog.cc
+++ b/src/wx/about_dialog.cc
@@ -27,7 +27,6 @@
 #include "static_text.h"
 #include "wx_util.h"
 #include "wx_variant.h"
-#include "lib/compose.hpp"
 #include "lib/variant.h"
 #include "lib/version.h"
 #include <dcp/warnings.h>
@@ -35,6 +34,7 @@ LIBDCP_DISABLE_WARNINGS
 #include <wx/notebook.h>
 #include <wx/hyperlink.h>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 
 using std::vector;
 
@@ -61,9 +61,9 @@ AboutDialog::AboutDialog (wxWindow* parent)
 
 	wxString s;
 	if (strcmp (dcpomatic_git_commit, "release") == 0) {
-		t = new StaticText (this, std_to_wx(String::compose("Version %1", dcpomatic_version)));
+		t = new StaticText(this, std_to_wx(fmt::format("Version {}", dcpomatic_version)));
 	} else {
-		t = new StaticText (this, std_to_wx(String::compose("Version %1 git %2", dcpomatic_version, dcpomatic_git_commit)));
+		t = new StaticText(this, std_to_wx(fmt::format("Version {} git {}", dcpomatic_version, dcpomatic_git_commit)));
 	}
 	t->SetFont (version_font);
 	sizer->Add (t, wxSizerFlags().Centre().Border(wxALL, 2));
diff --git a/src/wx/audio_plot.cc b/src/wx/audio_plot.cc
index ad478ddd0..6c5b7a26d 100644
--- a/src/wx/audio_plot.cc
+++ b/src/wx/audio_plot.cc
@@ -24,13 +24,13 @@
 #include "wx_util.h"
 #include "lib/audio_decoder.h"
 #include "lib/audio_analysis.h"
-#include "lib/compose.hpp"
 #include "lib/constants.h"
 #include "lib/maths_util.h"
 #include <dcp/warnings.h>
 LIBDCP_DISABLE_WARNINGS
 #include <wx/graphics.h>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 #include <boost/bind/bind.hpp>
 #include <cfloat>
 
@@ -197,7 +197,7 @@ AudioPlot::paint ()
 		int const y = (metrics.height - (i - _minimum) * metrics.y_scale) - metrics.y_origin;
 		h_grid.MoveToPoint (metrics.db_label_width - 4, y);
 		h_grid.AddLineToPoint (metrics.db_label_width + data_width, y);
-		gc->DrawText (std_to_wx (String::compose ("%1dB", i)), 0, y - (db_label_height / 2));
+		gc->DrawText(std_to_wx(fmt::format("{}dB", i)), 0, y - (db_label_height / 2));
 	}
 
 	wxColour const grid_colour = gui_is_dark() ? wxColour(80, 80, 80) : wxColour(200, 200, 200);
diff --git a/src/wx/barco_alchemy_certificate_panel.cc b/src/wx/barco_alchemy_certificate_panel.cc
index 34b2aa82e..a7f470ed3 100644
--- a/src/wx/barco_alchemy_certificate_panel.cc
+++ b/src/wx/barco_alchemy_certificate_panel.cc
@@ -23,8 +23,8 @@
 #include "download_certificate_dialog.h"
 #include "wx_util.h"
 #include "lib/internet.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 
 
@@ -61,8 +61,8 @@ BarcoAlchemyCertificatePanel::do_download ()
 {
 	string serial = wx_to_std (_serial->GetValue());
 	trim(serial);
-	string url = String::compose (
-		"sftp://%1:%2@certificates.barco.com/%3xxx/%4/Barco-ICMP.%5_cert.pem",
+	auto url = fmt::format(
+		"sftp://{}:{}@certificates.barco.com/{}xxx/{}/Barco-ICMP.{}_cert.pem",
 		Config::instance()->barco_username().get(),
 		Config::instance()->barco_password().get(),
 		serial.substr(0, 7),
diff --git a/src/wx/christie_certificate_panel.cc b/src/wx/christie_certificate_panel.cc
index 3536f5045..dc2c780b8 100644
--- a/src/wx/christie_certificate_panel.cc
+++ b/src/wx/christie_certificate_panel.cc
@@ -18,12 +18,14 @@
 
 */
 
+
 #include "christie_certificate_panel.h"
 #include "download_certificate_dialog.h"
 #include "wx_util.h"
 #include "lib/internet.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
+#include <fmt/format.h>
+
 
 using std::string;
 using boost::optional;
@@ -32,6 +34,7 @@ using boost::bind;
 using namespace boost::placeholders;
 #endif
 
+
 ChristieCertificatePanel::ChristieCertificatePanel (DownloadCertificateDialog* dialog)
 	: CredentialsDownloadCertificatePanel (
 			dialog,
@@ -50,8 +53,8 @@ ChristieCertificatePanel::ChristieCertificatePanel (DownloadCertificateDialog* d
 void
 ChristieCertificatePanel::do_download ()
 {
-	string const prefix = String::compose(
-		"ftp://%1:%2@certificates.christiedigital.com/Certificates/",
+	string const prefix = fmt::format(
+		"ftp://{}:{}@certificates.christiedigital.com/Certificates/",
 		Config::instance()->christie_username().get(),
 		Config::instance()->christie_password().get()
 		);
@@ -59,7 +62,7 @@ ChristieCertificatePanel::do_download ()
 	string serial = wx_to_std (_serial->GetValue());
 	serial.insert (0, 12 - serial.length(), '0');
 
-	string const url = String::compose ("%1F-IMB/F-IMB_%2_sha256.pem", prefix, serial);
+	string const url = fmt::format("{}F-IMB/F-IMB_{}_sha256.pem", prefix, serial);
 
 	optional<string> all_errors;
 	bool ok = true;
@@ -68,7 +71,7 @@ ChristieCertificatePanel::do_download ()
 	if (error) {
 		all_errors = *error;
 
-		auto const url = String::compose ("%1IMB-S2/IMB-S2_%2_sha256.pem", prefix, serial);
+		auto const url = fmt::format("{}IMB-S2/IMB-S2_{}_sha256.pem", prefix, serial);
 
 		error = get_from_url (url, true, false, boost::bind(&DownloadCertificatePanel::load_certificate_from_chain, this, _1, _2));
 		if (error) {
diff --git a/src/wx/closed_captions_dialog.cc b/src/wx/closed_captions_dialog.cc
index c8a04993c..5dcb0426a 100644
--- a/src/wx/closed_captions_dialog.cc
+++ b/src/wx/closed_captions_dialog.cc
@@ -23,11 +23,11 @@
 #include "film_viewer.h"
 #include "wx_util.h"
 #include "lib/butler.h"
-#include "lib/compose.hpp"
 #include "lib/constants.h"
 #include "lib/film.h"
 #include "lib/string_text.h"
 #include "lib/text_content.h"
+#include <fmt/format.h>
 #include <boost/bind/bind.hpp>
 
 
@@ -254,7 +254,7 @@ ClosedCaptionsDialog::update_tracks (shared_ptr<const Film> film)
 
 	_track->Clear ();
 	for (auto const& i: _tracks) {
-		_track->Append (std_to_wx(String::compose("%1 (%2)", i.name, i.language ? i.language->to_string() : wx_to_std(_("Unknown")))));
+		_track->Append(std_to_wx(fmt::format("{} ({})", i.name, i.language ? i.language->to_string() : wx_to_std(_("Unknown")))));
 	}
 
 	if (_track->GetCount() > 0) {
diff --git a/src/wx/dolby_doremi_certificate_panel.cc b/src/wx/dolby_doremi_certificate_panel.cc
index 24d8eb31a..95bdfc8bd 100644
--- a/src/wx/dolby_doremi_certificate_panel.cc
+++ b/src/wx/dolby_doremi_certificate_panel.cc
@@ -22,13 +22,13 @@
 #include "dolby_doremi_certificate_panel.h"
 #include "download_certificate_dialog.h"
 #include "wx_util.h"
-#include "lib/compose.hpp"
 #include "lib/internet.h"
 #include "lib/signal_manager.h"
 #include "lib/util.h"
 #include <dcp/raw_convert.h>
 #include <curl/curl.h>
 #include <zip.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 
 
@@ -66,28 +66,28 @@ DolbyDoremiCertificatePanel::DolbyDoremiCertificatePanel (DownloadCertificateDia
 static void
 try_common(vector<Location>& locations, string prefix, string serial)
 {
-	auto files = ls_url(String::compose("%1%2xxx/", prefix, serial.substr(0, 3)));
+	auto files = ls_url(fmt::format("{}{}xxx/", prefix, serial.substr(0, 3)));
 
 	auto check = [&locations, prefix, files, serial](string format, string file) {
-		auto const zip = String::compose(format, serial);
+		auto const zip = fmt::format(format, serial);
 		if (find(files.begin(), files.end(), zip) != files.end()) {
 			locations.push_back({
-				String::compose("%1%2xxx/%3", prefix, serial.substr(0, 3), zip),
-				String::compose(file, serial)
+				fmt::format("{}{}xxx/{}", prefix, serial.substr(0, 3), zip),
+				fmt::format(file, serial)
 			});
 		}
 	};
 
-	check("Dolby-DCP2000-%1.dcicerts.zip", "Dolby-DCP2000-%1.cert.sha256.pem");
-	check("Dolby-DCP2000-%1.certs.zip", "Dolby-DCP2000-%1.cert.sha256.pem");
-	check("dcp2000-%1.dcicerts.zip", "dcp2000-%1.cert.sha256.pem");
-	check("dcp2000-%1.certs.zip", "dcp2000-%1.cert.sha256.pem");
-	check("Dolby-IMB-%1.dcicerts.zip", "Dolby-IMB-%1.cert.sha256.pem");
-	check("imb-%1.dcicerts.zip", "imb-%1.cert.sha256.pem");
-	check("Dolby-IMS1000-%1.dcicerts.zip", "Dolby-IMS1000-%1.cert.sha256.pem");
-	check("Dolby-IMS2000-%1.dcicerts.zip", "Dolby-IMS2000-%1.cert.sha256.pem");
-	check("cert_Dolby-IMS3000-%1-SMPTE.zip", "cert_Dolby-IMS3000-%1-SMPTE.pem");
-	check("ims-%1.dcicerts.zip", "ims-%1.cert.sha256.pem");
+	check("Dolby-DCP2000-{}.dcicerts.zip", "Dolby-DCP2000-{}.cert.sha256.pem");
+	check("Dolby-DCP2000-{}.certs.zip", "Dolby-DCP2000-{}.cert.sha256.pem");
+	check("dcp2000-{}.dcicerts.zip", "dcp2000-{}.cert.sha256.pem");
+	check("dcp2000-{}.certs.zip", "dcp2000-{}.cert.sha256.pem");
+	check("Dolby-IMB-{}.dcicerts.zip", "Dolby-IMB-{}.cert.sha256.pem");
+	check("imb-{}.dcicerts.zip", "imb-{}.cert.sha256.pem");
+	check("Dolby-IMS1000-{}.dcicerts.zip", "Dolby-IMS1000-{}.cert.sha256.pem");
+	check("Dolby-IMS2000-{}.dcicerts.zip", "Dolby-IMS2000-{}.cert.sha256.pem");
+	check("cert_Dolby-IMS3000-{}-SMPTE.zip", "cert_Dolby-IMS3000-{}-SMPTE.pem");
+	check("ims-{}.dcicerts.zip", "ims-{}.cert.sha256.pem");
 }
 
 
@@ -103,12 +103,12 @@ try_cat862(vector<Location>& locations, string prefix, string serial)
 		cat862 = "CAT862_617000_and_higher";
 	} else {
 		int const lower = serial_int - (serial_int % 1000);
-		cat862 = String::compose ("CAT862_%1-%2", lower, lower + 999);
+		cat862 = fmt::format("CAT862_{}-{}", lower, lower + 999);
 	}
 
 	locations.push_back({
-		String::compose("%1%2/cert_Dolby256-CAT862-%3.zip", prefix, cat862, serial_int),
-		String::compose("cert_Dolby256-CAT862-%1.pem.crt", serial_int)
+		fmt::format("{}{}/cert_Dolby256-CAT862-{}.zip", prefix, cat862, serial_int),
+		fmt::format("cert_Dolby256-CAT862-{}.pem.crt", serial_int)
 	});
 }
 
@@ -125,12 +125,12 @@ try_dsp100(vector<Location>& locations, string prefix, string serial)
 		dsp100 = "DSP100_3000_and_higher";
 	} else {
 		int const lower = serial_int - (serial_int % 1000);
-		dsp100 = String::compose ("DSP100_%1_thru_%2", lower, lower + 999);
+		dsp100 = fmt::format("DSP100_{}_thru_{}", lower, lower + 999);
 	}
 
 	locations.push_back({
-		String::compose("%1%2/cert_Dolby256-DSP100-%3.zip", prefix, dsp100, serial_int),
-		String::compose("cert_Dolby256-DSP100-%1.pem.crt", serial_int)
+		fmt::format("{}{}/cert_Dolby256-DSP100-{}.zip", prefix, dsp100, serial_int),
+		fmt::format("cert_Dolby256-DSP100-{}.pem.crt", serial_int)
 	});
 }
 
@@ -147,12 +147,12 @@ try_cat745(vector<Location>& locations, string prefix, string serial)
 		cat745 = "CAT745_6000_and_higher";
 	} else {
 		int const lower = serial_int - (serial_int % 1000);
-		cat745 = String::compose("CAT745_%1_thru_%2", lower, lower + 999);
+		cat745 = fmt::format("CAT745_{}_thru_{}", lower, lower + 999);
 	}
 
 	locations.push_back({
-		String::compose("%1%2/cert_Dolby-CAT745-%3.zip", prefix, cat745, serial_int),
-		String::compose("cert_Dolby-CAT745-%1.pem.crt", serial_int)
+		fmt::format("{}{}/cert_Dolby-CAT745-{}.zip", prefix, cat745, serial_int),
+		fmt::format("cert_Dolby-CAT745-{}.pem.crt", serial_int)
 	});
 }
 
@@ -164,8 +164,8 @@ try_cp850(vector<Location>& locations, string prefix, string serial)
 
 	int const lower = serial_int - (serial_int % 1000);
 	locations.push_back({
-		String::compose ("%1CP850_CAT1600_F%2-F%3/cert_RMB_SPB_MDE_FMA.Dolby-CP850-F%4.zip", prefix, lower, lower + 999, serial_int),
-		String::compose ("cert_RMB_SPB_MDE_FMA.Dolby-CP850-F%1.pem.crt", serial_int)
+		fmt::format("{}CP850_CAT1600_F{}-F{}/cert_RMB_SPB_MDE_FMA.Dolby-CP850-F{}.zip", prefix, lower, lower + 999, serial_int),
+		fmt::format("cert_RMB_SPB_MDE_FMA.Dolby-CP850-F{}.pem.crt", serial_int)
 	});
 }
 
diff --git a/src/wx/download_certificate_panel.cc b/src/wx/download_certificate_panel.cc
index 8f826315d..9a955ca3b 100644
--- a/src/wx/download_certificate_panel.cc
+++ b/src/wx/download_certificate_panel.cc
@@ -22,11 +22,11 @@
 #include "download_certificate_dialog.h"
 #include "download_certificate_panel.h"
 #include "wx_util.h"
-#include "lib/compose.hpp"
 #include "lib/signal_manager.h"
 #include <dcp/certificate_chain.h>
 #include <dcp/exceptions.h>
 #include <dcp/util.h>
+#include <fmt/format.h>
 #include <boost/bind/bind.hpp>
 
 
@@ -64,7 +64,7 @@ DownloadCertificatePanel::load_certificate (boost::filesystem::path file, string
 		_certificate = dcp::Certificate (dcp::file_to_string(file));
 		_url = url;
 	} catch (dcp::MiscError& e) {
-		return String::compose(wx_to_std(_("Could not read certificate file (%1)")), e.what());
+		return fmt::format(wx_to_std(_("Could not read certificate file ({})")), e.what());
 	}
 	return {};
 }
@@ -77,7 +77,7 @@ DownloadCertificatePanel::load_certificate_from_chain (boost::filesystem::path f
 		_certificate = dcp::CertificateChain(dcp::file_to_string(file)).leaf();
 		_url = url;
 	} catch (dcp::MiscError& e) {
-		return String::compose(wx_to_std(_("Could not read certificate file (%1)")), e.what());
+		return fmt::format(wx_to_std(_("Could not read certificate file ({})")), e.what());
 	}
 	return {};
 }
diff --git a/src/wx/gdc_certificate_panel.cc b/src/wx/gdc_certificate_panel.cc
index 7e81c5a60..f5ae0ebe7 100644
--- a/src/wx/gdc_certificate_panel.cc
+++ b/src/wx/gdc_certificate_panel.cc
@@ -22,9 +22,9 @@
 #include "download_certificate_dialog.h"
 #include "gdc_certificate_panel.h"
 #include "wx_util.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/internet.h"
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 
 
@@ -56,8 +56,8 @@ GDCCertificatePanel::do_download ()
 {
 	string serial = wx_to_std (_serial->GetValue());
 	trim(serial);
-	string url = String::compose(
-		"ftp://%1:%2@ftp.gdc-tech.com/SHA256/%3.crt.pem",
+	string url = fmt::format(
+		"ftp://{}:{}@ftp.gdc-tech.com/SHA256/{}.crt.pem",
 		Config::instance()->gdc_username().get(),
 		Config::instance()->gdc_password().get(),
 		serial
diff --git a/src/wx/gl_video_view.cc b/src/wx/gl_video_view.cc
index 81156c67c..08bbce9b7 100644
--- a/src/wx/gl_video_view.cc
+++ b/src/wx/gl_video_view.cc
@@ -37,6 +37,7 @@
 #include "lib/exceptions.h"
 #include "lib/image.h"
 #include "lib/player_video.h"
+#include <fmt/format.h>
 #include <boost/bind/bind.hpp>
 #include <iostream>
 
@@ -109,7 +110,7 @@ GLVideoView::size_changed (wxSizeEvent const& ev)
 	int const width = std::round(ev.GetSize().GetWidth() * scale);
 	int const height = std::round(ev.GetSize().GetHeight() * scale);
 	_canvas_size = { width, height };
-	LOG_GENERAL("GLVideoView canvas size changed to %1x%2", width, height);
+	LOG_GENERAL("GLVideoView canvas size changed to {}x{}", width, height);
 	Sized ();
 }
 
@@ -435,7 +436,7 @@ GLVideoView::setup_shaders ()
 				log = string(log_char.data());
 			}
 			glDeleteShader(shader);
-			throw GLError(String::compose("Could not compile shader (%1)", log).c_str(), -1);
+			throw GLError(fmt::format("Could not compile shader ({})", log).c_str(), -1);
 		}
 		return shader;
 	};
@@ -463,7 +464,7 @@ GLVideoView::setup_shaders ()
 			log = string(log_char.data());
 		}
 		glDeleteProgram (program);
-		throw GLError(String::compose("Could not link shader (%1)", log).c_str(), -1);
+		throw GLError(fmt::format("Could not link shader ({})", log).c_str(), -1);
 	}
 	glDeleteShader (vertex_shader);
 	glDeleteShader (fragment_shader);
diff --git a/src/wx/name_format_editor.cc b/src/wx/name_format_editor.cc
index 166b0e145..4ecb3c302 100644
--- a/src/wx/name_format_editor.cc
+++ b/src/wx/name_format_editor.cc
@@ -23,7 +23,7 @@
 #include "static_text.h"
 #include "wx_util.h"
 #include "lib/util.h"
-
+#include <fmt/format.h>
 
 using std::string;
 
@@ -45,7 +45,7 @@ NameFormatEditor::NameFormatEditor (wxWindow* parent, dcp::NameFormat name, dcp:
 
 	auto titles_sizer = new wxFlexGridSizer (2);
 	for (auto const& i: titles) {
-		auto t = new StaticText (_panel, std_to_wx (String::compose ("%%%1 %2", i.first, i.second)));
+		auto t = new StaticText(_panel, std_to_wx(fmt::format("%{} {}", i.first, i.second)));
 		titles_sizer->Add(t, 1, wxRIGHT, DCPOMATIC_SIZER_X_GAP);
 		auto font = t->GetFont();
 		font.SetStyle (wxFONTSTYLE_ITALIC);
diff --git a/src/wx/player_information.cc b/src/wx/player_information.cc
index 9b8aafd18..997676663 100644
--- a/src/wx/player_information.cc
+++ b/src/wx/player_information.cc
@@ -23,11 +23,11 @@
 #include "wx_util.h"
 #include "film_viewer.h"
 #include "lib/playlist.h"
-#include "lib/compose.hpp"
 #include "lib/video_content.h"
 #include "lib/audio_content.h"
 #include "lib/dcp_content.h"
 #include "lib/film.h"
+#include <fmt/format.h>
 
 
 using std::cout;
@@ -178,8 +178,8 @@ PlayerInformation::triggered_update ()
 	vfr = dcp->video_frame_rate ();
 	DCPOMATIC_ASSERT (vfr);
 
-	auto const len = String::compose(
-		wx_to_std(_("Length: %1 (%2 frames)")),
+	auto const len = fmt::format(
+		wx_to_std(_("Length: {} ({} frames)")),
 		time_to_hmsf(dcp->full_length(_viewer.film()), lrint(*vfr)),
 		dcp->full_length(_viewer.film()).frames_round(*vfr)
 		);
diff --git a/src/wx/qube_certificate_panel.cc b/src/wx/qube_certificate_panel.cc
index de8fa8a49..696355d29 100644
--- a/src/wx/qube_certificate_panel.cc
+++ b/src/wx/qube_certificate_panel.cc
@@ -22,9 +22,9 @@
 #include "download_certificate_dialog.h"
 #include "qube_certificate_panel.h"
 #include "wx_util.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/internet.h"
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 
 
@@ -51,7 +51,7 @@ QubeCertificatePanel::QubeCertificatePanel (DownloadCertificateDialog* dialog, s
 void
 QubeCertificatePanel::do_download ()
 {
-	auto files = ls_url(String::compose("%1SMPTE-%2/", base, _type));
+	auto files = ls_url(fmt::format("{}SMPTE-{}/", base, _type));
 	if (files.empty()) {
 		error_dialog (this, _("Could not read certificates from Qube server."));
 		return;
@@ -62,7 +62,7 @@ QubeCertificatePanel::do_download ()
 
 	optional<string> name;
 	for (auto i: files) {
-		if (boost::algorithm::starts_with(i, String::compose("%1-%2-", _type, serial))) {
+		if (boost::algorithm::starts_with(i, fmt::format("{}-{}-", _type, serial))) {
 			name = i;
 			break;
 		}
@@ -74,7 +74,7 @@ QubeCertificatePanel::do_download ()
 		return;
 	}
 
-	auto error = get_from_url (String::compose("%1SMPTE-%2/%3", base, _type, *name), true, false, boost::bind(&DownloadCertificatePanel::load_certificate, this, _1, _2));
+	auto error = get_from_url(fmt::format("{}SMPTE-{}/{}", base, _type, *name), true, false, boost::bind(&DownloadCertificatePanel::load_certificate, this, _1, _2));
 
 	if (error) {
 		_dialog->message()->SetLabel({});
diff --git a/src/wx/simple_video_view.cc b/src/wx/simple_video_view.cc
index 84c837757..f6a9e3981 100644
--- a/src/wx/simple_video_view.cc
+++ b/src/wx/simple_video_view.cc
@@ -166,7 +166,7 @@ SimpleVideoView::timer ()
 		return;
 	}
 
-	LOG_DEBUG_VIDEO_VIEW("%1 -> %2; delay %3", next.seconds(), _viewer->time().seconds(), max((next.seconds() - _viewer->time().seconds()) * 1000, 1.0));
+	LOG_DEBUG_VIDEO_VIEW("{} -> {}; delay {}", next.seconds(), _viewer->time().seconds(), max((next.seconds() - _viewer->time().seconds()) * 1000, 1.0));
 	_timer.Start (max(1, time_until_next_frame().get_value_or(0)), wxTIMER_ONE_SHOT);
 
 	if (_viewer->butler()) {
diff --git a/src/wx/verify_dcp_result_panel.cc b/src/wx/verify_dcp_result_panel.cc
index 57f0f21e3..36905bf13 100644
--- a/src/wx/verify_dcp_result_panel.cc
+++ b/src/wx/verify_dcp_result_panel.cc
@@ -111,7 +111,7 @@ VerifyDCPResultPanel::fill(shared_ptr<VerifyDCPJob> job)
 			message.Replace(char_to_wx("%calculated_hash"), std_to_wx(note.calculated_hash().get()));
 		}
 		if (note.frame()) {
-			message.Replace(char_to_wx("%frame"), std_to_wx(dcp::fmt::to_string(note.frame().get())));
+			message.Replace(char_to_wx("%frame"), std_to_wx(fmt::to_string(note.frame().get())));
 			message.Replace(
 				char_to_wx("%timecode"),
 				std_to_wx(
@@ -125,13 +125,13 @@ VerifyDCPResultPanel::fill(shared_ptr<VerifyDCPJob> job)
 			message.Replace(char_to_wx("%f"), std_to_wx(note.file()->filename().string()));
 		}
 		if (note.line()) {
-			message.Replace(char_to_wx("%l"), std_to_wx(dcp::fmt::to_string(note.line().get())));
+			message.Replace(char_to_wx("%l"), std_to_wx(fmt::to_string(note.line().get())));
 		}
 		if (note.component()) {
-			message.Replace(char_to_wx("%component"), std_to_wx(dcp::fmt::to_string(note.component().get())));
+			message.Replace(char_to_wx("%component"), std_to_wx(fmt::to_string(note.component().get())));
 		}
 		if (note.size()) {
-			message.Replace(char_to_wx("%size"), std_to_wx(dcp::fmt::to_string(note.size().get())));
+			message.Replace(char_to_wx("%size"), std_to_wx(fmt::to_string(note.size().get())));
 		}
 		if (note.id()) {
 			message.Replace(char_to_wx("%id"), std_to_wx(note.id().get()));
diff --git a/src/wx/video_view.cc b/src/wx/video_view.cc
index c271cb65e..6f08b92c9 100644
--- a/src/wx/video_view.cc
+++ b/src/wx/video_view.cc
@@ -77,7 +77,7 @@ VideoView::get_next_frame (bool non_blocking)
 		Butler::Error e;
 		auto pv = butler->get_video (non_blocking ? Butler::Behaviour::NON_BLOCKING : Butler::Behaviour::BLOCKING, &e);
 		if (e.code == Butler::Error::Code::DIED) {
-			LOG_ERROR ("Butler died with %1", e.summary());
+			LOG_ERROR("Butler died with {}", e.summary());
 		}
 		if (!pv.first) {
 			return e.code == Butler::Error::Code::AGAIN ? AGAIN : FAIL;
diff --git a/src/wx/wx_util.cc b/src/wx/wx_util.cc
index fc8b3dc99..66ff200cc 100644
--- a/src/wx/wx_util.cc
+++ b/src/wx/wx_util.cc
@@ -48,6 +48,7 @@ LIBDCP_DISABLE_WARNINGS
 #include <wx/spinctrl.h>
 #include <wx/splash.h>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 #include <boost/thread.hpp>
 
 
@@ -758,7 +759,7 @@ bitmap_path (string name)
 wxString
 icon_path(string name)
 {
-	return gui_is_dark() ? bitmap_path(String::compose("%1_white.png", name)) : bitmap_path(String::compose("%1_black.png", name));
+	return gui_is_dark() ? bitmap_path(fmt::format("{}_white.png", name)) : bitmap_path(fmt::format("{}_black.png", name));
 }
 
 
diff --git a/test/audio_mapping_test.cc b/test/audio_mapping_test.cc
index 22412b260..c67ad64e5 100644
--- a/test/audio_mapping_test.cc
+++ b/test/audio_mapping_test.cc
@@ -25,10 +25,10 @@
  */
 
 
-#include <boost/test/unit_test.hpp>
 #include "lib/audio_mapping.h"
 #include "lib/constants.h"
-#include "lib/compose.hpp"
+#include <fmt/format.h>
+#include <boost/test/unit_test.hpp>
 
 
 using std::list;
@@ -72,7 +72,7 @@ guess_check (boost::filesystem::path filename, int output_channel)
 	AudioMapping m (1, 8);
 	m.make_default (0, filename);
 	for (int i = 0; i < 8; ++i) {
-		BOOST_TEST_INFO (String::compose("%1 channel %2", filename, i));
+		BOOST_TEST_INFO(fmt::format("{} channel {}", filename.string(), i));
 		BOOST_CHECK_CLOSE (m.get(0, i), i == output_channel ? 1 : 0, 0.01);
 	}
 }
diff --git a/test/burnt_subtitle_test.cc b/test/burnt_subtitle_test.cc
index 185f69839..6ba713f5d 100644
--- a/test/burnt_subtitle_test.cc
+++ b/test/burnt_subtitle_test.cc
@@ -46,6 +46,7 @@
 #include <dcp/reel_picture_asset.h>
 #include <dcp/reel_mono_picture_asset.h>
 #include <pango/pango-utils.h>
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 
 
@@ -157,8 +158,8 @@ BOOST_AUTO_TEST_CASE(burnt_subtitle_test_position)
 {
 	auto check = [](string alignment)
 	{
-		auto const name = String::compose("burnt_subtitle_test_position_%1", alignment);
-		auto subs = content_factory(String::compose("test/data/burn_%1.xml", alignment));
+		auto const name = fmt::format("burnt_subtitle_test_position_{}", alignment);
+		auto subs = content_factory(fmt::format("test/data/burn_{}.xml", alignment));
 		auto film = new_test_film(name, subs);
 		subs[0]->text[0]->set_use(true);
 		subs[0]->text[0]->set_burn(true);
@@ -171,11 +172,11 @@ BOOST_AUTO_TEST_CASE(burnt_subtitle_test_position)
 			});
 
 #if defined(DCPOMATIC_WINDOWS)
-		check_dcp(String::compose("test/data/windows/%1", name), film);
+		check_dcp(fmt::format("test/data/windows/{}", name), film);
 #elif defined(DCPOMATIC_OSX) || PANGO_VERSION_CHECK(1, 52, 1)
-		check_dcp(String::compose("test/data/mac/%1", name), film);
+		check_dcp(fmt::format("test/data/mac/{}", name), film);
 #else
-		check_dcp(String::compose("test/data/%1", name), film);
+		check_dcp(fmt::format("test/data/{}", name), film);
 #endif
 	};
 
diff --git a/test/cpl_hash_test.cc b/test/cpl_hash_test.cc
index 603fa4b8d..33d1ae0c5 100644
--- a/test/cpl_hash_test.cc
+++ b/test/cpl_hash_test.cc
@@ -30,6 +30,7 @@
 #include "lib/dcp_content.h"
 #include "lib/film.h"
 #include "test.h"
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <boost/test/unit_test.hpp>
 
@@ -50,7 +51,7 @@ BOOST_AUTO_TEST_CASE (hash_added_to_imported_dcp_test)
 	make_and_verify_dcp (ov);
 
 	/* Remove <Hash> tags from the CPL */
-	for (auto i: directory_iterator(String::compose("build/test/%1/%2", ov_name, ov->dcp_name()))) {
+	for (auto i: directory_iterator(fmt::format("build/test/{}/{}", ov_name, ov->dcp_name()))) {
 		if (boost::algorithm::starts_with(i.path().filename().string(), "cpl_")) {
 			dcp::File in(i.path(), "r");
 			BOOST_REQUIRE (in);
@@ -69,7 +70,7 @@ BOOST_AUTO_TEST_CASE (hash_added_to_imported_dcp_test)
 	}
 
 	string const vf_name = "hash_added_to_imported_dcp_test_vf";
-	auto ov_content = make_shared<DCPContent>(String::compose("build/test/%1/%2", ov_name, ov->dcp_name()));
+	auto ov_content = make_shared<DCPContent>(fmt::format("build/test/{}/{}", ov_name, ov->dcp_name()));
 	auto vf = new_test_film(
 		vf_name, { ov_content }
 		);
@@ -79,7 +80,7 @@ BOOST_AUTO_TEST_CASE (hash_added_to_imported_dcp_test)
 
 	/* Check for Hash tags in the VF DCP */
 	int hashes = 0;
-	for (auto i: directory_iterator(String::compose("build/test/%1/%2", vf_name, vf->dcp_name()))) {
+	for (auto i: directory_iterator(fmt::format("build/test/{}/{}", vf_name, vf->dcp_name()))) {
 		if (boost::algorithm::starts_with(i.path().filename().string(), "cpl_")) {
 			dcp::File in(i.path(), "r");
 			BOOST_REQUIRE (in);
diff --git a/test/digest_test.cc b/test/digest_test.cc
index 39737b7f5..c65ddacdd 100644
--- a/test/digest_test.cc
+++ b/test/digest_test.cc
@@ -25,7 +25,6 @@
  */
 
 
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/dcp_content_type.h"
 #include "lib/film.h"
@@ -34,6 +33,7 @@
 #include <dcp/cpl.h>
 #include <dcp/reel.h>
 #include <dcp/reel_picture_asset.h>
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 
 
@@ -45,7 +45,7 @@ using std::string;
 static string
 openssl_hash (boost::filesystem::path file)
 {
-	auto pipe = popen (String::compose ("openssl sha1 -binary %1 | openssl base64 -e", file.string()).c_str (), "r");
+	auto pipe = popen(fmt::format("openssl sha1 -binary {} | openssl base64 -e", file.string()).c_str (), "r");
 	BOOST_REQUIRE (pipe);
 	char buffer[128];
 	string output;
diff --git a/test/ffmpeg_encoder_test.cc b/test/ffmpeg_encoder_test.cc
index 0a48cd745..4e5ef924e 100644
--- a/test/ffmpeg_encoder_test.cc
+++ b/test/ffmpeg_encoder_test.cc
@@ -20,7 +20,6 @@
 
 
 #include "lib/audio_content.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/constants.h"
 #include "lib/content_factory.h"
@@ -40,6 +39,7 @@
 #include "test.h"
 #include <dcp/file.h>
 #include <dcp/raw_convert.h>
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 
 
@@ -77,7 +77,7 @@ ffmpeg_content_test (int number, boost::filesystem::path content, ExportFormat f
 		BOOST_REQUIRE (false);
 	}
 
-	name = String::compose("%1_test%2", name, number);
+	name = fmt::format("{}_test{}", name, number);
 
 	auto c = make_shared<FFmpegContent>(content);
 	auto film = new_test_film(name, {c}, &cl);
@@ -86,7 +86,7 @@ ffmpeg_content_test (int number, boost::filesystem::path content, ExportFormat f
 
 	film->write_metadata ();
 	auto job = make_shared<TranscodeJob>(film, TranscodeJob::ChangedBehaviour::IGNORE);
-	auto file = boost::filesystem::path("build") / "test" / String::compose("%1.%2", name, extension);
+	auto file = boost::filesystem::path("build") / "test" / fmt::format("{}.{}", name, extension);
 	cl.add (file);
 	FFmpegFilmEncoder encoder(film, job, file, format, false, false, false, 23);
 	encoder.go ();
diff --git a/test/ffmpeg_properties_test.cc b/test/ffmpeg_properties_test.cc
index 1e0cdc42f..b60b465bb 100644
--- a/test/ffmpeg_properties_test.cc
+++ b/test/ffmpeg_properties_test.cc
@@ -19,11 +19,11 @@
 */
 
 
-#include "lib/compose.hpp"
 #include "lib/content.h"
 #include "lib/content_factory.h"
 #include "lib/user_property.h"
 #include "test.h"
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 
 
@@ -37,7 +37,7 @@ colour_range_test(string name, boost::filesystem::path file, string ref)
 {
 	auto content = content_factory(file);
 	BOOST_REQUIRE(!content.empty());
-	auto film = new_test_film(String::compose("ffmpeg_properties_test_%1", name), { content.front() });
+	auto film = new_test_film(fmt::format("ffmpeg_properties_test_{}", name), { content.front() });
 
 	auto properties = content.front()->user_properties(film);
 	auto iter = std::find_if(properties.begin(), properties.end(), [](UserProperty const& property) { return property.key == "Colour range"; });
diff --git a/test/file_naming_test.cc b/test/file_naming_test.cc
index 2aa81cd4f..ee0c391bd 100644
--- a/test/file_naming_test.cc
+++ b/test/file_naming_test.cc
@@ -32,6 +32,7 @@
 #include "lib/ffmpeg_content.h"
 #include "lib/film.h"
 #include "lib/video_content.h"
+#include <fmt/format.h>
 #ifdef DCPOMATIC_WINDOWS
 #include <boost/locale.hpp>
 #endif
@@ -48,9 +49,9 @@ string
 mxf_regex(string part) {
 #ifdef DCPOMATIC_WINDOWS
 	/* Windows replaces . in filenames with _ */
-	return String::compose(".*flat_%1_png_.*\\.mxf", part);
+	return fmt::format(".*flat_{}_png_.*\\.mxf", part);
 #else
-	return String::compose(".*flat_%1\\.png_.*\\.mxf", part);
+	return fmt::format(".*flat_{}\\.png_.*\\.mxf", part);
 #endif
 };
 
diff --git a/test/hints_test.cc b/test/hints_test.cc
index 1b510f9e7..5c444903a 100644
--- a/test/hints_test.cc
+++ b/test/hints_test.cc
@@ -30,6 +30,7 @@
 #include "lib/hints.h"
 #include "lib/text_content.h"
 #include "test.h"
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 
 
@@ -98,7 +99,7 @@ BOOST_AUTO_TEST_CASE (hint_closed_caption_too_long)
 	check (
 		TextType::CLOSED_CAPTION,
 		"hint_closed_caption_too_long",
-		String::compose("At least one of your closed caption lines has more than %1 characters.  It is advisable to make each line %1 characters at most in length.", MAX_CLOSED_CAPTION_LENGTH, MAX_CLOSED_CAPTION_LENGTH)
+		fmt::format("At least one of your closed caption lines has more than {} characters.  It is advisable to make each line {} characters at most in length.", MAX_CLOSED_CAPTION_LENGTH, MAX_CLOSED_CAPTION_LENGTH)
 	      );
 }
 
@@ -108,7 +109,7 @@ BOOST_AUTO_TEST_CASE (hint_many_closed_caption_lines)
 	check (
 		TextType::CLOSED_CAPTION,
 		"hint_many_closed_caption_lines",
-		String::compose("Some of your closed captions span more than %1 lines, so they will be truncated.", MAX_CLOSED_CAPTION_LINES)
+		fmt::format("Some of your closed captions span more than {} lines, so they will be truncated.", MAX_CLOSED_CAPTION_LINES)
 	      );
 }
 
@@ -193,12 +194,12 @@ BOOST_AUTO_TEST_CASE (hint_subtitle_mxf_too_big)
 		}
 		fake_font.close();
 
-		auto content = content_factory(String::compose("test/data/%1%2.xml", name, i))[0];
+		auto content = content_factory(fmt::format("test/data/{}{}.xml", name, i))[0];
 		content->text[0]->set_type(TextType::OPEN_SUBTITLE);
 		content->text[0]->set_language(dcp::LanguageTag("en-US"));
 		film->examine_and_add_content(content);
 		BOOST_REQUIRE (!wait_for_jobs());
-		auto const font = content->text[0]->get_font(String::compose("font_%1", i));
+		auto const font = content->text[0]->get_font(fmt::format("font_{}", i));
 		BOOST_REQUIRE(font);
 		font->set_file("build/test/hint_subtitle_mxf_too_big.ttf");
 	}
@@ -220,7 +221,7 @@ BOOST_AUTO_TEST_CASE (hint_closed_caption_xml_too_big)
 
 	auto film = new_test_film(name);
 
-	dcp::File ccap(String::compose("build/test/%1.srt", name), "w");
+	dcp::File ccap(fmt::format("build/test/{}.srt", name), "w");
 	BOOST_REQUIRE (ccap);
 	for (int i = 0; i < 2048; ++i) {
 		fprintf(ccap.get(), "%d\n", i + 1);
diff --git a/test/image_filename_sorter_test.cc b/test/image_filename_sorter_test.cc
index 29b550753..aed8d7721 100644
--- a/test/image_filename_sorter_test.cc
+++ b/test/image_filename_sorter_test.cc
@@ -26,7 +26,7 @@
 
 
 #include "lib/image_filename_sorter.h"
-#include "lib/compose.hpp"
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 #include <algorithm>
 #include <random>
@@ -68,7 +68,7 @@ BOOST_AUTO_TEST_CASE (image_filename_sorter_test2)
 {
 	vector<boost::filesystem::path> paths;
 	for (int i = 0; i < 100000; ++i) {
-		paths.push_back(String::compose("some.filename.with.%1.number.tiff", i));
+		paths.push_back(fmt::format("some.filename.with.{}.number.tiff", i));
 	}
 
 	std::random_device rd;
@@ -77,6 +77,6 @@ BOOST_AUTO_TEST_CASE (image_filename_sorter_test2)
 
 	sort (paths.begin(), paths.end(), ImageFilenameSorter());
 	for (int i = 0; i < 100000; ++i) {
-		BOOST_CHECK_EQUAL(paths[i].string(), String::compose("some.filename.with.%1.number.tiff", i));
+		BOOST_CHECK_EQUAL(paths[i].string(), fmt::format("some.filename.with.{}.number.tiff", i));
 	}
 }
diff --git a/test/image_test.cc b/test/image_test.cc
index 4df4f9125..d69a8a909 100644
--- a/test/image_test.cc
+++ b/test/image_test.cc
@@ -26,7 +26,6 @@
  */
 
 
-#include "lib/compose.hpp"
 #include "lib/image.h"
 #include "lib/image_content.h"
 #include "lib/image_decoder.h"
@@ -34,6 +33,7 @@
 #include "lib/image_png.h"
 #include "lib/ffmpeg_image_proxy.h"
 #include "test.h"
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 #include <iostream>
 
@@ -512,7 +512,7 @@ BOOST_AUTO_TEST_CASE (crop_scale_window_test7)
 			Image::Alignment::PADDED,
 			false
 			);
-		path file = String::compose("crop_scale_window_test7-%1.png", left_crop);
+		path file = fmt::format("crop_scale_window_test7-{}.png", left_crop);
 		write_image(cropped, path("build") / "test" / file);
 		check_image(path("test") / "data" / file, path("build") / "test" / file, 10);
 	}
diff --git a/test/kdm_naming_test.cc b/test/kdm_naming_test.cc
index fe7da7f31..08e65f5b3 100644
--- a/test/kdm_naming_test.cc
+++ b/test/kdm_naming_test.cc
@@ -27,6 +27,7 @@
 #include "lib/kdm_with_metadata.h"
 #include "lib/screen.h"
 #include "test.h"
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 
 
@@ -133,7 +134,7 @@ BOOST_AUTO_TEST_CASE (single_kdm_naming_test)
 	boost::algorithm::replace_all (until_time, ":", "-");
 
 	auto const dcp_date = boost::gregorian::to_iso_string(film->isdcf_date());
-	auto const ref = String::compose("KDM_Cinema_A_-_Screen_1_-_MyGreatFilm_TST-1_F_XX-XX_MOS_2K_%1_SMPTE_OV_-_%2_%3_-_%4_%5.xml", dcp_date, from.date(), from_time, until.date(), until_time);
+	auto const ref = fmt::format("KDM_Cinema_A_-_Screen_1_-_MyGreatFilm_TST-1_F_XX-XX_MOS_2K_{}_SMPTE_OV_-_{}_{}_-_{}_{}.xml", dcp_date, from.date(), from_time, until.date(), until_time);
 	BOOST_CHECK_MESSAGE (boost::filesystem::exists("build/test/single_kdm_naming_test/" + ref), "File " << ref << " not found");
 }
 
@@ -218,41 +219,41 @@ BOOST_AUTO_TEST_CASE(directory_kdm_naming_test)
 	boost::algorithm::replace_all (until_time, ":", "-");
 
 	auto const dcp_date = boost::gregorian::to_iso_string(film->isdcf_date());
-	auto const dcp_name = String::compose("MyGreatFilm_TST-1_F_XX-XX_MOS_2K_%1_SMPTE_OV", dcp_date);
-	auto const common = String::compose("%1_-_%2_%3_-_%4_%5", dcp_name, from.date(), from_time, until.date(), until_time);
+	auto const dcp_name = fmt::format("MyGreatFilm_TST-1_F_XX-XX_MOS_2K_{}_SMPTE_OV", dcp_date);
+	auto const common = fmt::format("{}_-_{}_{}_-_{}_{}", dcp_name, from.date(), from_time, until.date(), until_time);
 
 	path const base = "build/test/directory_kdm_naming_test";
 
-	path dir_a = String::compose("Cinema_A_-_%s_-_%1", common);
+	path dir_a = fmt::format("Cinema_A_-_%s_-_{}", common);
 	BOOST_CHECK_MESSAGE (boost::filesystem::exists(base / dir_a), "Directory " << dir_a << " not found");
-	path dir_b = String::compose("Cinema_B_-_%s_-_%1", common);
+	path dir_b = fmt::format("Cinema_B_-_%s_-_{}", common);
 	BOOST_CHECK_MESSAGE (boost::filesystem::exists(base / dir_b), "Directory " << dir_b << " not found");
 
 #ifdef DCPOMATIC_WINDOWS
-	path ref = String::compose("KDM_%1.xml", dcp_name);
+	path ref = fmt::format("KDM_{}.xml", dcp_name);
 #else
-	path ref = String::compose("KDM_Cinema_A_-_Screen_2_-_%1_-_%2.xml", common, cpl_id);
+	path ref = fmt::format("KDM_Cinema_A_-_Screen_2_-_{}_-_{}.xml", common, cpl_id);
 #endif
 	BOOST_CHECK_MESSAGE (boost::filesystem::exists(base / dir_a / ref), "File " << ref << " not found");
 
 #ifdef DCPOMATIC_WINDOWS
-	ref = String::compose("KDM_%1.xml", dcp_name);
+	ref = fmt::format("KDM_{}.xml", dcp_name);
 #else
-	ref = String::compose("KDM_Cinema_B_-_Screen_X_-_%1_-_%2.xml", common, cpl_id);
+	ref = fmt::format("KDM_Cinema_B_-_Screen_X_-_{}_-_{}.xml", common, cpl_id);
 #endif
 	BOOST_CHECK_MESSAGE (boost::filesystem::exists(base / dir_b / ref), "File " << ref << " not found");
 
 #ifdef DCPOMATIC_WINDOWS
-	ref = String::compose("KDM_%1.xml", dcp_name);
+	ref = fmt::format("KDM_{}.xml", dcp_name);
 #else
-	ref = String::compose("KDM_Cinema_A_-_Screen_1_-_%1_-_%2.xml", common, cpl_id);
+	ref = fmt::format("KDM_Cinema_A_-_Screen_1_-_{}_-_{}.xml", common, cpl_id);
 #endif
 	BOOST_CHECK_MESSAGE (boost::filesystem::exists(base / dir_a / ref), "File " << ref << " not found");
 
 #ifdef DCPOMATIC_WINDOWS
-	ref = String::compose("KDM_%1.xml", dcp_name);
+	ref = fmt::format("KDM_{}.xml", dcp_name);
 #else
-	ref = String::compose("KDM_Cinema_B_-_Screen_Z_-_%1_-_%2.xml", common, cpl_id);
+	ref = fmt::format("KDM_Cinema_B_-_Screen_Z_-_{}_-_{}.xml", common, cpl_id);
 #endif
 	BOOST_CHECK_MESSAGE (boost::filesystem::exists(base / dir_b / ref), "File " << ref << " not found");
 }
diff --git a/test/map_cli_test.cc b/test/map_cli_test.cc
index aaf5b944f..0cea9ae9e 100644
--- a/test/map_cli_test.cc
+++ b/test/map_cli_test.cc
@@ -32,6 +32,7 @@
 #include <dcp/reel.h>
 #include <dcp/reel_picture_asset.h>
 #include <dcp/reel_sound_asset.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <boost/filesystem.hpp>
 #include <boost/optional.hpp>
@@ -90,7 +91,7 @@ find_cpl(boost::filesystem::path dir)
 BOOST_AUTO_TEST_CASE(map_simple_dcp_copy)
 {
 	string const name = "map_simple_dcp_copy";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto content = content_factory("test/data/flat_red.png");
 	auto film = new_test_film(name + "_in", content);
@@ -120,7 +121,7 @@ BOOST_AUTO_TEST_CASE(map_simple_dcp_copy)
 BOOST_AUTO_TEST_CASE(map_simple_dcp_copy_by_id)
 {
 	string const name = "map_simple_dcp_copy_by_id";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto content = content_factory("test/data/flat_red.png");
 	auto film = new_test_film(name + "_in", content);
@@ -152,7 +153,7 @@ BOOST_AUTO_TEST_CASE(map_simple_dcp_copy_by_id)
 BOOST_AUTO_TEST_CASE(map_simple_dcp_copy_with_symlinks)
 {
 	string const name = "map_simple_dcp_copy_with_symlinks";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto content = content_factory("test/data/flat_red.png");
 	auto film = new_test_film(name + "_in", content);
@@ -185,7 +186,7 @@ BOOST_AUTO_TEST_CASE(map_simple_dcp_copy_with_symlinks)
 BOOST_AUTO_TEST_CASE(map_simple_dcp_copy_with_hardlinks)
 {
 	string const name = "map_simple_dcp_copy_with_hardlinks";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto content = content_factory("test/data/flat_red.png");
 	auto film = new_test_film(name + "_in", content);
@@ -216,7 +217,7 @@ BOOST_AUTO_TEST_CASE(map_simple_dcp_copy_with_hardlinks)
 BOOST_AUTO_TEST_CASE(map_simple_interop_dcp_with_subs)
 {
 	string const name = "map_simple_interop_dcp_with_subs";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto picture = content_factory("test/data/flat_red.png").front();
 	auto subs = content_factory("test/data/15s.srt").front();
@@ -247,7 +248,7 @@ void
 test_map_ov_vf_copy(vector<string> extra_args = {})
 {
 	string const name = "map_ov_vf_copy";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto ov_content = content_factory("test/data/flat_red.png");
 	auto ov_film = new_test_film(name + "_ov", ov_content);
@@ -298,7 +299,7 @@ BOOST_AUTO_TEST_CASE(map_ov_vf_copy)
 BOOST_AUTO_TEST_CASE(map_ov_vf_copy_multiple_reference)
 {
 	string const name = "map_ov_vf_copy_multiple_reference";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto ov_content = content_factory("test/data/flat_red.png");
 	auto ov_film = new_test_film(name + "_ov", ov_content);
@@ -346,7 +347,7 @@ BOOST_AUTO_TEST_CASE(map_simple_dcp_copy_with_rename)
 	ConfigRestorer cr;
 	Config::instance()->set_dcp_asset_filename_format(dcp::NameFormat("hello%c"));
 	string const name = "map_simple_dcp_copy_with_rename";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto content = content_factory("test/data/flat_red.png");
 	auto film = new_test_film(name + "_in", content);
@@ -394,7 +395,7 @@ static
 void
 test_two_cpls_each_with_subs(string name, bool interop)
 {
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	vector<dcp::VerificationNote::Code> acceptable_errors;
 	if (interop) {
@@ -408,7 +409,7 @@ test_two_cpls_each_with_subs(string name, bool interop)
 	for (auto i = 0; i < 2; ++i) {
 		auto picture = content_factory("test/data/flat_red.png").front();
 		auto subs = content_factory("test/data/15s.srt").front();
-		films[i] = new_test_film(String::compose("%1_%2_in", name, i), { picture, subs });
+		films[i] = new_test_film(fmt::format("{}_{}_in", name, i), { picture, subs });
 		films[i]->set_interop(interop);
 		subs->only_text()->set_language(dcp::LanguageTag("de"));
 		make_and_verify_dcp(films[i], acceptable_errors);
@@ -450,7 +451,7 @@ BOOST_AUTO_TEST_CASE(map_with_given_config)
 	ConfigRestorer cr;
 
 	string const name = "map_with_given_config";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto content = content_factory("test/data/flat_red.png");
 	auto film = new_test_film(name + "_in", content);
@@ -480,7 +481,7 @@ BOOST_AUTO_TEST_CASE(map_with_given_config)
 BOOST_AUTO_TEST_CASE(map_multireel_interop_ov_and_vf_adding_ccaps)
 {
 	string const name = "map_multireel_interop_ov_and_vf_adding_ccaps";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	vector<shared_ptr<Content>> video = {
 		content_factory("test/data/flat_red.png")[0],
@@ -545,7 +546,7 @@ BOOST_AUTO_TEST_CASE(map_uses_config_for_issuer_and_creator)
 	Config::instance()->set_dcp_creator("Fred");
 
 	string const name = "map_uses_config_for_issuer_and_creator";
-	string const out = String::compose("build/test/%1_out", name);
+	string const out = fmt::format("build/test/{}_out", name);
 
 	auto content = content_factory("test/data/flat_red.png");
 	auto film = new_test_film(name + "_in", content);
diff --git a/test/markers_test.cc b/test/markers_test.cc
index f7ff3a6b5..caa2f7cc9 100644
--- a/test/markers_test.cc
+++ b/test/markers_test.cc
@@ -50,7 +50,7 @@ BOOST_AUTO_TEST_CASE (automatic_ffoc_lfoc_markers_test1)
 	film->set_interop (false);
 	make_and_verify_dcp (film);
 
-	dcp::DCP dcp (String::compose("build/test/%1/%2", name, film->dcp_name()));
+	dcp::DCP dcp(fmt::format("build/test/{}/{}", name, film->dcp_name()));
 	dcp.read ();
 	BOOST_REQUIRE_EQUAL (dcp.cpls().size(), 1U);
 	auto cpl = dcp.cpls().front();
@@ -86,7 +86,7 @@ BOOST_AUTO_TEST_CASE (automatic_ffoc_lfoc_markers_test2)
 			dcp::VerificationNote::Code::INCORRECT_LFOC
 		});
 
-	dcp::DCP dcp (String::compose("build/test/%1/%2", name, film->dcp_name()));
+	dcp::DCP dcp(fmt::format("build/test/{}/{}", name, film->dcp_name()));
 	dcp.read ();
 	BOOST_REQUIRE_EQUAL (dcp.cpls().size(), 1U);
 	auto cpl = dcp.cpls().front();
@@ -116,7 +116,7 @@ BOOST_AUTO_TEST_CASE(markers_correct_with_reels)
 	film->set_reel_type(ReelType::BY_VIDEO_CONTENT);
 	make_and_verify_dcp(film);
 
-	dcp::DCP dcp(String::compose("build/test/%1/%2", name, film->dcp_name()));
+	dcp::DCP dcp(fmt::format("build/test/{}/{}", name, film->dcp_name()));
 	dcp.read ();
 	BOOST_REQUIRE_EQUAL(dcp.cpls().size(), 1U);
 	auto cpl = dcp.cpls()[0];
diff --git a/test/player_test.cc b/test/player_test.cc
index cac5dffe9..a91bf6268 100644
--- a/test/player_test.cc
+++ b/test/player_test.cc
@@ -28,7 +28,6 @@
 #include "lib/audio_buffers.h"
 #include "lib/audio_content.h"
 #include "lib/butler.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/constants.h"
 #include "lib/content_factory.h"
@@ -46,6 +45,7 @@
 #include "lib/text_content.h"
 #include "lib/video_content.h"
 #include "test.h"
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 #include <boost/algorithm/string.hpp>
 #include <iostream>
@@ -225,12 +225,12 @@ BOOST_AUTO_TEST_CASE (player_seek_test)
 		butler->seek (t, true);
 		auto video = butler->get_video(Butler::Behaviour::BLOCKING, 0);
 		BOOST_CHECK_EQUAL(video.second.get(), t.get());
-		write_image(video.first->image(bind(PlayerVideo::force, AV_PIX_FMT_RGB24), VideoRange::FULL, true), String::compose("build/test/player_seek_test_%1.png", i));
+		write_image(video.first->image(bind(PlayerVideo::force, AV_PIX_FMT_RGB24), VideoRange::FULL, true), fmt::format("build/test/player_seek_test_{}.png", i));
 		/* This 14.08 is empirically chosen (hopefully) to accept changes in rendering between the reference and a test machine
 		   (17.10 and 16.04 seem to anti-alias a little differently) but to reject gross errors e.g. missing fonts or missing
 		   text altogether.
 		*/
-		check_image(TestPaths::private_data() / String::compose("player_seek_test_%1.png", i), String::compose("build/test/player_seek_test_%1.png", i), 14.08);
+		check_image(TestPaths::private_data() / fmt::format("player_seek_test_{}.png", i), fmt::format("build/test/player_seek_test_{}.png", i), 14.08);
 	}
 }
 
@@ -261,9 +261,9 @@ BOOST_AUTO_TEST_CASE (player_seek_test2)
 		auto video = butler->get_video(Butler::Behaviour::BLOCKING, 0);
 		BOOST_CHECK_EQUAL(video.second.get(), t.get());
 		write_image(
-			video.first->image(bind(PlayerVideo::force, AV_PIX_FMT_RGB24), VideoRange::FULL, true), String::compose("build/test/player_seek_test2_%1.png", i)
+			video.first->image(bind(PlayerVideo::force, AV_PIX_FMT_RGB24), VideoRange::FULL, true), fmt::format("build/test/player_seek_test2_{}.png", i)
 			);
-		check_image(TestPaths::private_data() / String::compose("player_seek_test2_%1.png", i), String::compose("build/test/player_seek_test2_%1.png", i), 14.08);
+		check_image(TestPaths::private_data() / fmt::format("player_seek_test2_{}.png", i), fmt::format("build/test/player_seek_test2_{}.png", i), 14.08);
 	}
 }
 
diff --git a/test/socket_test.cc b/test/socket_test.cc
index c7d43e812..395e5f720 100644
--- a/test/socket_test.cc
+++ b/test/socket_test.cc
@@ -127,7 +127,7 @@ BOOST_AUTO_TEST_CASE (socket_basic_test)
 
 	boost::asio::io_service io_service;
 	tcp::resolver resolver (io_service);
-	tcp::resolver::query query("127.0.0.1", dcp::fmt::to_string(TEST_SERVER_PORT));
+	tcp::resolver::query query("127.0.0.1", fmt::to_string(TEST_SERVER_PORT));
 	tcp::resolver::iterator endpoint_iterator = resolver.resolve (query);
 
 	auto socket = make_shared<Socket>();
@@ -149,7 +149,7 @@ BOOST_AUTO_TEST_CASE (socket_digest_test1)
 
 	boost::asio::io_service io_service;
 	tcp::resolver resolver (io_service);
-	tcp::resolver::query query("127.0.0.1", dcp::fmt::to_string(TEST_SERVER_PORT));
+	tcp::resolver::query query("127.0.0.1", fmt::to_string(TEST_SERVER_PORT));
 	tcp::resolver::iterator endpoint_iterator = resolver.resolve (query);
 
 	shared_ptr<Socket> socket(new Socket);
@@ -178,7 +178,7 @@ BOOST_AUTO_TEST_CASE (socket_digest_test2)
 
 	boost::asio::io_service io_service;
 	tcp::resolver resolver (io_service);
-	tcp::resolver::query query("127.0.0.1", dcp::fmt::to_string(TEST_SERVER_PORT));
+	tcp::resolver::query query("127.0.0.1", fmt::to_string(TEST_SERVER_PORT));
 	tcp::resolver::iterator endpoint_iterator = resolver.resolve (query);
 
 	shared_ptr<Socket> socket(new Socket);
diff --git a/test/subtitle_language_test.cc b/test/subtitle_language_test.cc
index a1a45eb42..258d4f907 100644
--- a/test/subtitle_language_test.cc
+++ b/test/subtitle_language_test.cc
@@ -60,7 +60,7 @@ BOOST_AUTO_TEST_CASE (subtitle_language_interop_test)
 		false
 		);
 
-	check_dcp(String::compose("test/data/%1", name), String::compose("build/test/%1/%2", name, film->dcp_name()));
+	check_dcp(fmt::format("test/data/{}", name), fmt::format("build/test/{}/{}", name, film->dcp_name()));
 }
 
 
@@ -87,7 +87,7 @@ BOOST_AUTO_TEST_CASE (subtitle_language_smpte_test)
 	 * differences in sound between the DCP and the reference to avoid test
 	 * failures for unrelated reasons.
 	 */
-	check_dcp(String::compose("test/data/%1", name), String::compose("build/test/%1/%2", name, film->dcp_name()), true);
+	check_dcp(fmt::format("test/data/{}", name), fmt::format("build/test/{}/{}", name, film->dcp_name()), true);
 }
 
 
diff --git a/test/subtitle_position_test.cc b/test/subtitle_position_test.cc
index 05e305478..55288a6ca 100644
--- a/test/subtitle_position_test.cc
+++ b/test/subtitle_position_test.cc
@@ -28,6 +28,7 @@
 #include <dcp/interop_text_asset.h>
 #include <dcp/language_tag.h>
 #include <dcp/smpte_text_asset.h>
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 #include <vector>
 
@@ -112,8 +113,8 @@ vpos_test(dcp::VAlign reference, float position, dcp::SubtitleStandard from, dcp
 			break;
 	}
 
-	auto name = String::compose("vpos_test_%1_%2", standard, valign_to_string(reference));
-	auto in = content_factory(String::compose("test/data/%1.xml", name));
+	auto name = fmt::format("vpos_test_{}_{}", standard, valign_to_string(reference));
+	auto in = content_factory(fmt::format("test/data/{}.xml", name));
 	auto film = new_test_film(name, in);
 
 	film->set_interop(to == dcp::Standard::INTEROP);
diff --git a/test/subtitle_reel_number_test.cc b/test/subtitle_reel_number_test.cc
index 48174d012..96225617f 100644
--- a/test/subtitle_reel_number_test.cc
+++ b/test/subtitle_reel_number_test.cc
@@ -30,7 +30,7 @@
 #include <dcp/reel.h>
 #include <dcp/interop_text_asset.h>
 #include <dcp/reel_text_asset.h>
-#include <fmt/period.h>
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 
 
@@ -66,7 +66,7 @@ BOOST_AUTO_TEST_CASE (subtitle_reel_number_test)
 		if (i->main_subtitle()) {
 			auto ass = dynamic_pointer_cast<dcp::InteropTextAsset>(i->main_subtitle()->asset());
 			BOOST_REQUIRE (ass);
-			BOOST_CHECK_EQUAL(ass->reel_number(), dcp::fmt::to_string(n));
+			BOOST_CHECK_EQUAL(ass->reel_number(), fmt::to_string(n));
 			++n;
 		}
 	}
diff --git a/test/test.cc b/test/test.cc
index fe0286799..9d04e1b8f 100644
--- a/test/test.cc
+++ b/test/test.cc
@@ -25,7 +25,6 @@
  */
 
 
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/cross.h"
 #include "lib/dcp_content_type.h"
@@ -592,7 +591,7 @@ check_xml(
 	auto test_children = test->get_children ();
 	string context;
 	if (ref_file && test_file) {
-		context = String::compose(" comparing %1 and %2", ref_file->string(), test_file->string());
+		context = fmt::format(" comparing {} and {}", ref_file->string(), test_file->string());
 	}
 	BOOST_REQUIRE_MESSAGE (
 		ref_children.size() == test_children.size(),
@@ -734,7 +733,7 @@ png_flush (png_structp)
 static void
 png_error_fn (png_structp, char const * message)
 {
-	throw EncodeError (String::compose("Error during PNG write: %1", message));
+	throw EncodeError(fmt::format("Error during PNG write: {}", message));
 }
 
 
@@ -817,7 +816,7 @@ write_image (shared_ptr<const Image> image, boost::filesystem::path file)
 void
 check_ffmpeg (boost::filesystem::path ref, boost::filesystem::path check, int audio_tolerance)
 {
-	int const r = system (String::compose("ffcmp -t %1 %2 %3", audio_tolerance, ref.string(), check.string()).c_str());
+	int const r = system(fmt::format("ffcmp -t {} {} {}", audio_tolerance, ref.string(), check.string()).c_str());
 	BOOST_REQUIRE_EQUAL (WEXITSTATUS(r), 0);
 }
 
@@ -1010,13 +1009,13 @@ make_and_verify_dcp(shared_ptr<Film> film, vector<dcp::VerificationNote::Code> i
 	auto dcp_inspect_env = getenv("DCPOMATIC_DCP_INSPECT");
 	if (dcp_inspect && dcp_inspect_env) {
 		boost::filesystem::path dcp_inspect(dcp_inspect_env);
-		auto cmd = String::compose("%1 %2 > %3 2>&1", dcp_inspect, film->dir(film->dcp_name()), film->file("dcp_inspect.log"));
+		auto cmd = fmt::format("{} {} > {} 2>&1", dcp_inspect.string(), film->dir(film->dcp_name()).string(), film->file("dcp_inspect.log").string());
 		auto result = system(cmd.c_str());
 		BOOST_CHECK_EQUAL(WEXITSTATUS(result), 0);
 	}
 
 	if (clairmeta && getenv("DCPOMATIC_CLAIRMETA")) {
-		auto cmd = String::compose("python3 -m clairmeta.cli check -type dcp %1 > %2 2>&1", film->dir(film->dcp_name()), film->file("clairmeta.log"));
+		auto cmd = fmt::format("python3 -m clairmeta.cli check -type dcp {} > {} 2>&1", film->dir(film->dcp_name()).string(), film->file("clairmeta.log").string());
 		auto result = system(cmd.c_str());
 		BOOST_CHECK_EQUAL(WEXITSTATUS(result), 0);
 	}
diff --git a/test/threed_test.cc b/test/threed_test.cc
index 27dd12cbe..dcf5cfd11 100644
--- a/test/threed_test.cc
+++ b/test/threed_test.cc
@@ -44,6 +44,7 @@
 #include "test.h"
 #include <dcp/mono_j2k_picture_asset.h>
 #include <dcp/stereo_j2k_picture_asset.h>
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 #include <iostream>
 
@@ -209,7 +210,7 @@ BOOST_AUTO_TEST_CASE (threed_test7)
 		}
 	}
 	BOOST_REQUIRE (failed);
-	BOOST_CHECK_EQUAL (failed->error_summary(), String::compose("The content file %1 is set as 3D but does not appear to contain 3D images.  Please set it to 2D.  You can still make a 3D DCP from this content by ticking the 3D option in the DCP video tab.", boost::filesystem::canonical(content_path).string()));
+	BOOST_CHECK_EQUAL(failed->error_summary(), fmt::format("The content file {} is set as 3D but does not appear to contain 3D images.  Please set it to 2D.  You can still make a 3D DCP from this content by ticking the 3D option in the DCP video tab.", boost::filesystem::canonical(content_path).string()));
 
 	while (signal_manager->ui_idle ()) {}
author	Carl Hetherington <cth@carlh.net>	2024-12-23 21:53:32 +0100
committer	Carl Hetherington <cth@carlh.net>	2024-12-26 00:27:08 +0100
commit	8caf013a9b8d709ed7c3d5e9febee0067e6fcf1f (patch)
tree	40da87cb357e8b1c54a1464bdbac2d014640e30c
parent	cec6ff92aef45c687085ecfc1059004407c18c57 (diff)