Replace String::compose with fmt.

author: Carl Hetherington <cth@carlh.net> 2025-07-09 01:49:10 +0200
committer: Carl Hetherington <cth@carlh.net> 2025-07-09 21:29:57 +0200
commit: fe5bed524942c1ffc157f8a5ef59f5d291789891 (patch)
tree: cf3ed3ed7672ab3c38673fa0d15927d80ed0c5d2
parent: bb07c53c501365b6380ae2c7e1a149b955d13d4d (diff)
77 files changed, 324 insertions, 323 deletions
diff --git a/src/lib/analyse_audio_job.cc b/src/lib/analyse_audio_job.cc
index d2c3b04e5..eb3fcecb7 100644
--- a/src/lib/analyse_audio_job.cc
+++ b/src/lib/analyse_audio_job.cc
@@ -21,7 +21,6 @@
 
 #include "analyse_audio_job.h"
 #include "audio_analysis.h"
-#include "compose.hpp"
 #include "dcpomatic_log.h"
 #include "film.h"
 #include "filter.h"
diff --git a/src/lib/audio_decoder.cc b/src/lib/audio_decoder.cc
index 60b0f07ad..6520f8175 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"
diff --git a/src/lib/butler.cc b/src/lib/butler.cc
index 5edd84115..17eb48b34 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"
@@ -28,6 +27,7 @@
 #include "player.h"
 #include "util.h"
 #include "video_content.h"
+#include <fmt/format.h>
 
 
 using std::cout;
@@ -104,7 +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(&dcpomatic::io_context::run, &_prepare_context));
@@ -140,10 +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()));
 		}
 	}
 
@@ -152,19 +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) {
@@ -324,9 +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)
@@ -472,7 +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 8673f9c8b..7bea7ad95 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>
@@ -156,7 +157,7 @@ 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 21e89fd78..b349eb490 100644
--- a/src/lib/collator.cc
+++ b/src/lib/collator.cc
@@ -29,6 +29,7 @@
 #include <unicode/ustring.h>
 #include <fmt/format.h>
 #include <boost/scoped_array.hpp>
+#include <algorithm>
 #include <cstring>
 #include <vector>
 
@@ -102,8 +103,8 @@ Collator::find(string pattern, string text) const
 		usearch_close(search);
 		return index != -1;
 	} else {
-		transform(pattern.begin(), pattern.end(), pattern.begin(), ::tolower);
-		transform(text.begin(), text.end(), text.begin(), ::tolower);
+		std::transform(pattern.begin(), pattern.end(), pattern.begin(), ::tolower);
+		std::transform(text.begin(), text.end(), text.begin(), ::tolower);
 		return pattern.find(text) != string::npos;
 	}
 }
diff --git a/src/lib/config.cc b/src/lib/config.cc
index 5f3f2f6fe..5ad0f16d8 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"
@@ -276,7 +275,7 @@ 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;
diff --git a/src/lib/content.cc b/src/lib/content.cc
index 2a69adefd..196288f4a 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"
@@ -296,9 +295,9 @@ 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;
 }
@@ -452,7 +451,7 @@ 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 fa3f0876c..0b419098c 100644
--- a/src/lib/content_factory.cc
+++ b/src/lib/content_factory.cc
@@ -39,7 +39,6 @@
 #include "string_text_file_content.h"
 #include "util.h"
 #include "video_mxf_content.h"
-#include "compose.hpp"
 #include <libcxml/cxml.h>
 #include <dcp/filesystem.h>
 #include <dcp/smpte_text_asset.h>
diff --git a/src/lib/copy_to_drive_job.cc b/src/lib/copy_to_drive_job.cc
index 4ed9421d6..504a3ae9e 100644
--- a/src/lib/copy_to_drive_job.cc
+++ b/src/lib/copy_to_drive_job.cc
@@ -77,9 +77,9 @@ CopyToDriveJob::run ()
 		LOG_DISK("%1", 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/create_cli.cc b/src/lib/create_cli.cc
index 51518ae82..df040e134 100644
--- a/src/lib/create_cli.cc
+++ b/src/lib/create_cli.cc
@@ -20,7 +20,6 @@
 
 
 #include "audio_content.h"
-#include "compose.hpp"
 #include "config.h"
 #include "content_factory.h"
 #include "create_cli.h"
@@ -61,8 +60,8 @@ help()
 	DCPOMATIC_ASSERT(colour_conversions.length() > 2);
 	colour_conversions = colour_conversions.substr(0, colour_conversions.length() - 2);
 
-	return string("\nSyntax: %1 [OPTION] <CONTENT> [OPTION] [<CONTENT> ...]\n") +
-		variant::insert_dcpomatic("  -v, --version                 show %1 version\n") +
+	return 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"
@@ -107,7 +106,7 @@ 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;
 	}
 
@@ -126,7 +125,7 @@ argument_option(int& n, int argc, char* argv[], string short_name, string long_n
 	}
 
 	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;
 	}
 
@@ -155,14 +154,14 @@ 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;
 	}
@@ -203,7 +202,7 @@ 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;
 		}
 
@@ -312,7 +311,7 @@ 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 {
 				if (next_colour_conversion) {
@@ -368,7 +367,7 @@ 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;
 		}
 	}
@@ -376,7 +375,7 @@ CreateCLI::CreateCLI(int argc, char* argv[])
 	if (!container_ratio_string.empty()) {
 		_container_ratio = Ratio::from_id_if_exists(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;
 		}
 	}
@@ -387,21 +386,21 @@ 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;
 	}
 
@@ -410,7 +409,7 @@ 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_linux.cc b/src/lib/cross_linux.cc
index ccd78a3b1..a50b4a21f 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"
@@ -31,6 +30,7 @@
 #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>
@@ -114,7 +114,7 @@ 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());
+	auto const ffprobe = fmt::format("ffprobe {} \"{}\" {} \"{}\"", args.empty() ? " " : args, content.string(), redirect, out.string());
 	LOG_GENERAL (N_("Probing with %1"), ffprobe);
 	int const r = system (ffprobe.c_str());
 	if (r == -1 || (WIFEXITED(r) && WEXITSTATUS(r) != 0)) {
@@ -336,12 +336,12 @@ 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/curl_uploader.cc b/src/lib/curl_uploader.cc
index 753c66496..b62830bde 100644
--- a/src/lib/curl_uploader.cc
+++ b/src/lib/curl_uploader.cc
@@ -94,7 +94,7 @@ 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");
diff --git a/src/lib/dcp_text_track.cc b/src/lib/dcp_text_track.cc
index ec1d6828b..ef3890401 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->as_string() : _("Unknown"));
+	return fmt::format("{} ({})", name, language ? language->as_string() : _("Unknown"));
 }
 
 void
diff --git a/src/lib/disk_writer_messages.cc b/src/lib/disk_writer_messages.cc
index 0a11ce618..562e9e876 100644
--- a/src/lib/disk_writer_messages.cc
+++ b/src/lib/disk_writer_messages.cc
@@ -72,24 +72,24 @@ 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 = 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 = 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 = fmt::format("{}\n", DISK_WRITER_VERIFY_PROGRESS);
 			message += fmt::to_string(_progress) + "\n";
 			break;
 	}
diff --git a/src/lib/email.cc b/src/lib/email.cc
index 1333b9e2d..4f926eef7 100644
--- a/src/lib/email.cc
+++ b/src/lib/email.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "dcpomatic_log.h"
 #include "email.h"
@@ -27,6 +26,7 @@
 #include "util.h"
 #include "variant.h"
 #include <curl/curl.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 
 #include "i18n.h"
@@ -205,9 +205,9 @@ 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()) {
@@ -247,7 +247,7 @@ 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/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 5f0fe935a..c0cf5a815 100644
--- a/src/lib/exceptions.cc
+++ b/src/lib/exceptions.cc
@@ -47,7 +47,7 @@ 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)
 {
 
@@ -118,7 +118,7 @@ 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)
 {
@@ -127,7 +127,7 @@ 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)
 {
@@ -136,7 +136,7 @@ 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))
 {
 
 }
@@ -150,7 +150,7 @@ 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)
@@ -167,7 +167,7 @@ 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)
 {
diff --git a/src/lib/exceptions.h b/src/lib/exceptions.h
index dae64fb5d..b1daa0624 100644
--- a/src/lib/exceptions.h
+++ b/src/lib/exceptions.h
@@ -28,10 +28,10 @@
 #define DCPOMATIC_EXCEPTIONS_H
 
 
-#include "compose.hpp"
 extern "C" {
 #include <libavutil/pixfmt.h>
 }
+#include <fmt/format.h>
 #include <boost/filesystem.hpp>
 #include <boost/optional.hpp>
 #include <sqlite3.h>
@@ -54,19 +54,19 @@ 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()))
 	{}
 };
 
@@ -91,11 +91,11 @@ public:
 	{}
 
 	explicit EncodeError (std::string function, std::string caller)
-		: std::runtime_error (String::compose("%1 failed [%2]", function, 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))
+		: std::runtime_error(fmt::format("{} failed [{}] ({})", function, caller, error))
 	{}
 };
 
@@ -110,7 +110,7 @@ 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)
 	{}
 
@@ -343,7 +343,7 @@ class CPLNotFoundError : public DCPError
 {
 public:
 	CPLNotFoundError(std::string id)
-		: DCPError(String::compose("CPL %1 not found", id))
+		: DCPError(fmt::format("CPL {} not found", id))
 	{}
 };
 
@@ -514,17 +514,17 @@ private:
 
 	std::string get_message(SQLiteDatabase& 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(SQLiteDatabase& 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(SQLiteDatabase& 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 7dfc2b856..0eba706db 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"
@@ -58,6 +57,7 @@ extern "C" {
 #include <lwext4/ext4_mbr.h>
 #include <lwext4/ext4_mkfs.h>
 }
+#include <fmt/format.h>
 #include <boost/filesystem.hpp>
 #include <chrono>
 #include <string>
@@ -114,13 +114,13 @@ 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 +134,7 @@ 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 +147,7 @@ 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 +171,12 @@ 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 +188,7 @@ read(boost::filesystem::path from, boost::filesystem::path to, uint64_t& total_r
 		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 +228,7 @@ 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 +238,7 @@ copy(boost::filesystem::path from, boost::filesystem::path to, uint64_t& total_r
 	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 +247,7 @@ copy(boost::filesystem::path from, boost::filesystem::path to, uint64_t& total_r
 		}
 	} 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 %3", from.string(), cr.generic_string(), write_digest);
 		copied_files.push_back(CopiedFile(from, cr, write_digest));
 	}
 }
@@ -260,7 +260,7 @@ 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 %3 on write, now %4", 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 +348,7 @@ 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 %3", 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 +426,17 @@ 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): {} {} %3", 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/fcpxml.cc b/src/lib/fcpxml.cc
index 49798381c..a52385571 100644
--- a/src/lib/fcpxml.cc
+++ b/src/lib/fcpxml.cc
@@ -22,6 +22,7 @@
 #include "fcpxml.h"
 #include <dcp/raw_convert.h>
 #include <libcxml/cxml.h>
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <boost/filesystem.hpp>
 
@@ -41,7 +42,7 @@ convert_time(string const& time)
 	boost::algorithm::split(parts, time, boost::is_any_of("/"));
 
 	if (parts.size() != 2 || parts[1].empty() || parts[1][parts[1].length() - 1] != 's') {
-		throw FCPXMLError(String::compose("Unexpected time format %1", time));
+		throw FCPXMLError(fmt::format("Unexpected time format {}", time));
 	}
 
 	return dcpomatic::ContentTime{dcp::raw_convert<int64_t>(parts[0]) * dcpomatic::ContentTime::HZ / dcp::raw_convert<int64_t>(parts[1])};
@@ -66,7 +67,7 @@ dcpomatic::fcpxml::load(boost::filesystem::path xml_file)
 		auto name = video->string_attribute("name");
 		auto iter = assets.find(name);
 		if (iter == assets.end()) {
-			throw FCPXMLError(String::compose(_("Video refers to missing asset %1"), name));
+			throw FCPXMLError(fmt::format(_("Video refers to missing asset {}"), name));
 		}
 
 		auto start = convert_time(video->string_attribute("offset"));
diff --git a/src/lib/ffmpeg.cc b/src/lib/ffmpeg.cc
index c6867c081..696527379 100644
--- a/src/lib/ffmpeg.cc
+++ b/src/lib/ffmpeg.cc
@@ -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 95aa63ba4..ddf880b03 100644
--- a/src/lib/ffmpeg_content.cc
+++ b/src/lib/ffmpeg_content.cc
@@ -380,8 +380,8 @@ 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
 		);
 }
 
diff --git a/src/lib/file_group.cc b/src/lib/file_group.cc
index 56a5c2c59..6c4a768e8 100644
--- a/src/lib/file_group.cc
+++ b/src/lib/file_group.cc
@@ -24,12 +24,12 @@
  */
 
 
-#include "compose.hpp"
 #include "cross.h"
 #include "dcpomatic_assert.h"
 #include "exceptions.h"
 #include "file_group.h"
 #include <dcp/filesystem.h>
+#include <fmt/format.h>
 #include <sndfile.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/image_png.cc b/src/lib/image_png.cc
index e56b68d9a..0909dd2f2 100644
--- a/src/lib/image_png.cc
+++ b/src/lib/image_png.cc
@@ -22,6 +22,7 @@
 #include "dcpomatic_assert.h"
 #include "exceptions.h"
 #include "image.h"
+#include <fmt/format.h>
 #include <png.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/j2k_encoder.cc b/src/lib/j2k_encoder.cc
index 50452fbad..f1a2f2337 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"
diff --git a/src/lib/job.cc b/src/lib/job.cc
index ee6ad4e70..885df5645 100644
--- a/src/lib/job.cc
+++ b/src/lib/job.cc
@@ -105,7 +105,7 @@ Job::start ()
 void
 Job::run_wrapper ()
 {
-	start_of_thread (String::compose("Job-%1", json_name()));
+	start_of_thread(fmt::format("Job-{}", json_name()));
 
 	try {
 
diff --git a/src/lib/kdm_cli.cc b/src/lib/kdm_cli.cc
index 50bf9ea51..64b467e22 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())
 	{}
 };
 
@@ -130,7 +131,7 @@ 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") {
@@ -143,7 +144,7 @@ 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));
 }
 
 
@@ -176,7 +177,7 @@ 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(
@@ -185,7 +186,7 @@ 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()));
 		}
 	}
 }
@@ -230,10 +231,10 @@ 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 */
@@ -294,7 +295,7 @@ 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()));
 	}
 }
 
@@ -424,7 +425,7 @@ 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()));
 	}
 }
 
@@ -623,7 +624,7 @@ 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) {
@@ -644,7 +645,7 @@ 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 {};
 	}
@@ -711,7 +712,7 @@ try
 	}
 
 	if (verbose) {
-		out(String::compose("Making KDMs valid from %1 to %2", boost::posix_time::to_simple_string(valid_from.get()), boost::posix_time::to_simple_string(valid_to.get())));
+		out(fmt::format("Making KDMs valid from {} to {}", boost::posix_time::to_simple_string(valid_from.get()), boost::posix_time::to_simple_string(valid_to.get())));
 	}
 
 	string const thing = argv[optind];
diff --git a/src/lib/map_cli.cc b/src/lib/map_cli.cc
index 20d5ce6af..43023a440 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..6252b40d1 100644
--- a/src/lib/nanomsg.cc
+++ b/src/lib/nanomsg.cc
@@ -24,6 +24,7 @@
 #include "nanomsg.h"
 #include <nanomsg/nn.h>
 #include <nanomsg/pair.h>
+#include <fmt/format.h>
 #include <cerrno>
 #include <stdexcept>
 
@@ -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 516a66ee2..bb22067a6 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>
@@ -801,7 +801,7 @@ 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;
@@ -1469,7 +1469,7 @@ 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/reel_writer.cc b/src/lib/reel_writer.cc
index bd326e853..a9566b5c7 100644
--- a/src/lib/reel_writer.cc
+++ b/src/lib/reel_writer.cc
@@ -483,7 +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);
@@ -529,7 +529,7 @@ ReelWriter::create_reel_picture(shared_ptr<dcp::Reel> reel, list<ReferencedReelA
 	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);
@@ -581,7 +581,7 @@ ReelWriter::create_reel_sound(shared_ptr<dcp::Reel> reel, list<ReferencedReelAss
 		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)
 				);
 		}
 
diff --git a/src/lib/text_decoder.cc b/src/lib/text_decoder.cc
index 52d6c58d3..c159c00ca 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"
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/types.cc b/src/lib/types.cc
index 28d58f36b..7247a726a 100644
--- a/src/lib/types.cc
+++ b/src/lib/types.cc
@@ -19,7 +19,6 @@
 */
 
 #include "types.h"
-#include "compose.hpp"
 #include "dcpomatic_assert.h"
 #include <dcp/cpl.h>
 #include <dcp/dcp.h>
diff --git a/src/lib/unzipper.cc b/src/lib/unzipper.cc
index 8d468f24f..00431ff1b 100644
--- a/src/lib/unzipper.cc
+++ b/src/lib/unzipper.cc
@@ -19,6 +19,7 @@
 */
 
 
+#include "compose.hpp"
 #include "dcpomatic_assert.h"
 #include "exceptions.h"
 #include "unzipper.h"
diff --git a/src/lib/upload_job.cc b/src/lib/upload_job.cc
index 3019b7662..1cb778667 100644
--- a/src/lib/upload_job.cc
+++ b/src/lib/upload_job.cc
@@ -24,7 +24,6 @@
  */
 
 
-#include "compose.hpp"
 #include "config.h"
 #include "curl_uploader.h"
 #include "dcpomatic_log.h"
diff --git a/src/lib/util.cc b/src/lib/util.cc
index eeab9f2d6..89f8b79d5 100644
--- a/src/lib/util.cc
+++ b/src/lib/util.cc
@@ -410,7 +410,7 @@ 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);
 }
 
 
@@ -462,7 +462,7 @@ LIBDCP_ENABLE_WARNINGS
 	if (running_tests) {
 		putenv("FONTCONFIG_PATH=fonts");
 	} else {
-		putenv(String::compose("FONTCONFIG_PATH=%1", resources_path().string()).c_str());
+		putenv(fmt::format("FONTCONFIG_PATH={}", resources_path().string()).c_str());
 	}
 #endif
 
@@ -1029,7 +1029,7 @@ 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());
 }
 
 
diff --git a/src/lib/video_content.cc b/src/lib/video_content.cc
index 3f2819082..408524551 100644
--- a/src/lib/video_content.cc
+++ b/src/lib/video_content.cc
@@ -362,16 +362,16 @@ 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;
@@ -526,7 +526,7 @@ 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_ring_buffers.cc b/src/lib/video_ring_buffers.cc
index 5f355c1ab..e78a60df7 100644
--- a/src/lib/video_ring_buffers.cc
+++ b/src/lib/video_ring_buffers.cc
@@ -19,19 +19,19 @@
 */
 
 
-#include "video_ring_buffers.h"
 #include "player_video.h"
-#include "compose.hpp"
+#include "video_ring_buffers.h"
+#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 72a6eaf8b..5681a5a6d 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"
@@ -44,6 +43,7 @@
 #include <dcp/locale_convert.h>
 #include <dcp/reel_file_asset.h>
 #include <dcp/reel_text_asset.h>
+#include <fmt/format.h>
 #include <cerrno>
 #include <cfloat>
 #include <set>
@@ -393,9 +393,9 @@ 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
@@ -406,12 +406,12 @@ 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, frame %1, eyes %2"), i.frame, static_cast<int>(i.eyes));
+						LOG_WARNING(N_("- type FAKE, frame {}, eyes {}"), i.frame, static_cast<int>(i.eyes));
 					}
 				}
 			}
@@ -433,7 +433,7 @@ 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) {
 					/* Get the data back from disk where we stored it temporarily */
 					qi.encoded = make_shared<ArrayData>(film()->j2c_path(qi.reel, qi.frame, qi.eyes, false));
@@ -442,12 +442,12 @@ 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.frame, qi.eyes);
 				++_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;
@@ -472,7 +472,7 @@ try
 			DCPOMATIC_ASSERT(item != _queue.rend());
 			++_pushed_to_disk;
 
-			LOG_GENERAL("Writer full; pushes %1 to disk while awaiting %2", item->frame, _last_written[_queue.front().reel].frame() + 1);
+			LOG_GENERAL("Writer full; pushes {} to disk while awaiting {}", item->frame, _last_written[_queue.front().reel].frame() + 1);
 
 			item->encoded->write_via_temp(
 				film()->j2c_path(item->reel, item->frame, item->eyes, true),
@@ -613,12 +613,12 @@ 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);
@@ -709,7 +709,7 @@ Writer::finish()
 	dcp.write_xml(signer, Config::instance()->dcp_metadata_filename_format(), group_id);
 
 	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, %4 pushed to disk"), _full_written, _fake_written, _repeat_written, _pushed_to_disk
 		);
 
 	write_cover_sheet();
@@ -759,13 +759,13 @@ 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");
@@ -779,11 +779,11 @@ 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 7b9d55ef4..b2c3673ad 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 d8e79d667..af1738888 100644
--- a/src/tools/dcpomatic.cc
+++ b/src/tools/dcpomatic.cc
@@ -1488,7 +1488,7 @@ 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_disk.cc b/src/tools/dcpomatic_disk.cc
index 56b30590f..f726412f1 100644
--- a/src/tools/dcpomatic_disk.cc
+++ b/src/tools/dcpomatic_disk.cc
@@ -49,6 +49,7 @@
 LIBDCP_DISABLE_WARNINGS
 #include <boost/process.hpp>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 #ifdef DCPOMATIC_WINDOWS
 #include <boost/process/windows.hpp>
 #endif
@@ -252,7 +253,7 @@ 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
 
diff --git a/src/tools/dcpomatic_disk_writer.cc b/src/tools/dcpomatic_disk_writer.cc
index 3bb6fcd3f..c7dc69e1d 100644
--- a/src/tools/dcpomatic_disk_writer.cc
+++ b/src/tools/dcpomatic_disk_writer.cc
@@ -19,7 +19,6 @@
 */
 
 
-#include "lib/compose.hpp"
 #include "lib/cross.h"
 #include "lib/dcpomatic_log.h"
 #include "lib/digester.h"
diff --git a/src/tools/dcpomatic_kdm.cc b/src/tools/dcpomatic_kdm.cc
index d596f8ca2..eb5d90893 100644
--- a/src/tools/dcpomatic_kdm.cc
+++ b/src/tools/dcpomatic_kdm.cc
@@ -42,7 +42,6 @@
 #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"
diff --git a/src/tools/dcpomatic_player.cc b/src/tools/dcpomatic_player.cc
index 9fb4a049b..2c0acb13c 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"
@@ -90,6 +89,7 @@ LIBDCP_ENABLE_WARNINGS
 #ifdef __WXGTK__
 #include <X11/Xlib.h>
 #endif
+#include <fmt/format.h>
 #include <boost/algorithm/string.hpp>
 #include <boost/bind/bind.hpp>
 #include <iostream>
@@ -1181,7 +1181,7 @@ 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 e5d8b0a90..effa3a885 100644
--- a/src/tools/dcpomatic_server.cc
+++ b/src/tools/dcpomatic_server.cc
@@ -44,6 +44,7 @@ LIBDCP_DISABLE_WARNINGS
 #include <wx/splash.h>
 #include <wx/taskbar.h>
 LIBDCP_ENABLE_WARNINGS
+#include <fmt/format.h>
 #include <boost/optional.hpp>
 #include <boost/thread.hpp>
 #include <iostream>
@@ -253,7 +254,7 @@ 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/wx/about_dialog.cc b/src/wx/about_dialog.cc
index 2abf0ef17..c4cbde70a 100644
--- a/src/wx/about_dialog.cc
+++ b/src/wx/about_dialog.cc
@@ -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/christie_certificate_panel.cc b/src/wx/christie_certificate_panel.cc
index 3536f5045..360691335 100644
--- a/src/wx/christie_certificate_panel.cc
+++ b/src/wx/christie_certificate_panel.cc
@@ -22,12 +22,13 @@
 #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;
 using boost::bind;
+using boost::optional;
 #if BOOST_VERSION >= 106100
 using namespace boost::placeholders;
 #endif
@@ -50,8 +51,8 @@ ChristieCertificatePanel::ChristieCertificatePanel (DownloadCertificateDialog* d
 void
 ChristieCertificatePanel::do_download ()
 {
-	string const prefix = String::compose(
-		"ftp://%1:%2@certificates.christiedigital.com/Certificates/",
+	auto const prefix = fmt::format(
+		"ftp://{}:{}@certificates.christiedigital.com/Certificates/",
 		Config::instance()->christie_username().get(),
 		Config::instance()->christie_password().get()
 		);
@@ -59,7 +60,7 @@ 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);
+	auto const url = fmt::format("{}F-IMB/F-IMB_{}_sha256.pem", prefix, serial);
 
 	optional<string> all_errors;
 	bool ok = true;
@@ -68,7 +69,7 @@ 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/content_sub_panel.cc b/src/wx/content_sub_panel.cc
index 10fdfa232..8b60c740e 100644
--- a/src/wx/content_sub_panel.cc
+++ b/src/wx/content_sub_panel.cc
@@ -23,7 +23,6 @@
 #include "content_panel.h"
 #include "wx_util.h"
 #include "lib/dcp_content.h"
-#include "lib/compose.hpp"
 #include "lib/log.h"
 #include <dcp/warnings.h>
 LIBDCP_DISABLE_WARNINGS
diff --git a/src/wx/content_timeline_dialog.cc b/src/wx/content_timeline_dialog.cc
index 697e6561f..4d1bbb1d4 100644
--- a/src/wx/content_timeline_dialog.cc
+++ b/src/wx/content_timeline_dialog.cc
@@ -23,7 +23,6 @@
 #include "content_timeline_dialog.h"
 #include "film_editor.h"
 #include "wx_util.h"
-#include "lib/compose.hpp"
 #include "lib/cross.h"
 #include "lib/film.h"
 #include "lib/playlist.h"
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/film_viewer.cc b/src/wx/film_viewer.cc
index 7b22999b0..45476c75d 100644
--- a/src/wx/film_viewer.cc
+++ b/src/wx/film_viewer.cc
@@ -34,7 +34,6 @@
 #include "simple_video_view.h"
 #include "wx_util.h"
 #include "lib/butler.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/dcp_content.h"
 #include "lib/dcpomatic_log.h"
diff --git a/src/wx/gl_video_view.cc b/src/wx/gl_video_view.cc
index 4ca5af21a..08e1e2521 100644
--- a/src/wx/gl_video_view.cc
+++ b/src/wx/gl_video_view.cc
@@ -443,7 +443,7 @@ 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 (%1)", log).c_str(), -1);
 		}
 		return shader;
 	};
@@ -471,7 +471,7 @@ 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 (%1)", log).c_str(), -1);
 	}
 	glDeleteShader(vertex_shader);
 	glDeleteShader(fragment_shader);
diff --git a/src/wx/job_view.cc b/src/wx/job_view.cc
index aa175816d..7ed44ee1e 100644
--- a/src/wx/job_view.cc
+++ b/src/wx/job_view.cc
@@ -27,7 +27,6 @@
 #include "wx_util.h"
 #include "wx_variant.h"
 #include "lib/analyse_audio_job.h"
-#include "lib/compose.hpp"
 #include "lib/config.h"
 #include "lib/job.h"
 #include "lib/job_manager.h"
diff --git a/src/wx/playlist_controls.cc b/src/wx/playlist_controls.cc
index 87a0e9a4a..c7dad4139 100644
--- a/src/wx/playlist_controls.cc
+++ b/src/wx/playlist_controls.cc
@@ -26,7 +26,6 @@
 #include "static_text.h"
 #include "wx_util.h"
 #include "wx_variant.h"
-#include "lib/compose.hpp"
 #include "lib/constants.h"
 #include "lib/cross.h"
 #include "lib/dcp_content.h"
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/screen_dialog.cc b/src/wx/screen_dialog.cc
index 21786b8a2..84d798065 100644
--- a/src/wx/screen_dialog.cc
+++ b/src/wx/screen_dialog.cc
@@ -26,7 +26,6 @@
 #include "static_text.h"
 #include "table_dialog.h"
 #include "wx_util.h"
-#include "lib/compose.hpp"
 #include "lib/util.h"
 #include <dcp/warnings.h>
 #include <dcp/exceptions.h>
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 6b2e64d6a..9010d7983 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>
 
 
@@ -153,8 +154,8 @@ 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);
@@ -167,11 +168,11 @@ 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)
-		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 2953046b5..482119542 100644
--- a/test/file_naming_test.cc
+++ b/test/file_naming_test.cc
@@ -48,9 +48,9 @@ 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 4735ef75e..71a8c3e56 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>
 
 
@@ -136,7 +137,7 @@ 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");
 }
 
@@ -224,41 +225,41 @@ 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..37ba3c999 100644
--- a/test/markers_test.cc
+++ b/test/markers_test.cc
@@ -32,6 +32,7 @@
 #include <dcp/dcp.h>
 #include <dcp/reel_markers_asset.h>
 #include <dcp/reel.h>
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 
 
@@ -50,7 +51,7 @@ 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 +87,7 @@ 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 +117,7 @@ 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 384a73ebc..3d98e6f42 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(AV_PIX_FMT_RGB24, VideoRange::FULL, true), String::compose("build/test/player_seek_test_%1.png", i));
+		write_image(video.first->image(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(AV_PIX_FMT_RGB24, VideoRange::FULL, true), String::compose("build/test/player_seek_test2_%1.png", i)
+			video.first->image(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/subtitle_language_test.cc b/test/subtitle_language_test.cc
index 789412912..06eb32d94 100644
--- a/test/subtitle_language_test.cc
+++ b/test/subtitle_language_test.cc
@@ -30,6 +30,7 @@
 #include "lib/text_content.h"
 #include "test.h"
 #include <dcp/language_tag.h>
+#include <fmt/format.h>
 #include <boost/test/unit_test.hpp>
 #include <vector>
 
@@ -60,7 +61,7 @@ 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 +88,7 @@ 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/test.cc b/test/test.cc
index 553c4587a..124c43ba5 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"
@@ -61,6 +60,7 @@
 extern "C" {
 #include <libavformat/avformat.h>
 }
+#include <fmt/format.h>
 #define BOOST_TEST_DYN_LINK
 #define BOOST_TEST_MODULE dcpomatic_test
 #include <boost/algorithm/string.hpp>
@@ -594,7 +594,7 @@ 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(),
@@ -739,7 +739,7 @@ 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));
 }
 
 
@@ -822,7 +822,7 @@ 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);
 }
 
@@ -1015,13 +1015,13 @@ 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 5508eb735..6e666bcf6 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>	2025-07-09 01:49:10 +0200
committer	Carl Hetherington <cth@carlh.net>	2025-07-09 21:29:57 +0200
commit	fe5bed524942c1ffc157f8a5ef59f5d291789891 (patch)
tree	cf3ed3ed7672ab3c38673fa0d15927d80ed0c5d2
parent	bb07c53c501365b6380ae2c7e1a149b955d13d4d (diff)