More fixes for errors / crashes / misbehaviour with content changes

and the butler.

Here we signal both before and after a change in content.  Before,
the player disables itself so that any pass()/seek() will be no-ops.
After, the player rebuilds its pieces and the butler re-seeks to
get back to where it was before the change.

17 files changed, 183 insertions, 115 deletions

diff --git a/src/lib/audio_content.cc b/src/lib/audio_content.cc
index 7f0ec1fd6..703696a44 100644
--- a/src/lib/audio_content.cc
+++ b/src/lib/audio_content.cc
@@ -146,6 +146,8 @@ AudioContent::technical_summary () const
 void
 AudioContent::set_mapping (AudioMapping mapping)
 {
+	ContentChange cc (_parent, AudioContentProperty::STREAMS);
+
 	int c = 0;
 	BOOST_FOREACH (AudioStreamPtr i, streams ()) {
 		AudioMapping stream_mapping (i->channels (), MAX_DCP_AUDIO_CHANNELS);
@@ -157,8 +159,6 @@ AudioContent::set_mapping (AudioMapping mapping)
 		}
 		i->set_mapping (stream_mapping);
 	}
-
-	_parent->signal_changed (AudioContentProperty::STREAMS);
 }
 
 AudioMapping
@@ -341,12 +341,12 @@ AudioContent::add_properties (list<UserProperty>& p) const
 void
 AudioContent::set_streams (vector<AudioStreamPtr> streams)
 {
+	ContentChange cc (_parent, AudioContentProperty::STREAMS);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_streams = streams;
 	}
-
-	_parent->signal_changed (AudioContentProperty::STREAMS);
 }
 
 AudioStreamPtr
@@ -360,24 +360,24 @@ AudioContent::stream () const
 void
 AudioContent::add_stream (AudioStreamPtr stream)
 {
+	ContentChange cc (_parent, AudioContentProperty::STREAMS);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_streams.push_back (stream);
 	}
-
-	_parent->signal_changed (AudioContentProperty::STREAMS);
 }
 
 void
 AudioContent::set_stream (AudioStreamPtr stream)
 {
+	ContentChange cc (_parent, AudioContentProperty::STREAMS);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_streams.clear ();
 		_streams.push_back (stream);
 	}
-
-	_parent->signal_changed (AudioContentProperty::STREAMS);
 }
 
 void
diff --git a/src/lib/butler.cc b/src/lib/butler.cc
index 6789d74a5..386e7f9db 100644
--- a/src/lib/butler.cc
+++ b/src/lib/butler.cc
@@ -64,7 +64,8 @@ Butler::Butler (shared_ptr<Player> player, shared_ptr<Log> log, AudioMapping aud
 	_player_video_connection = _player->Video.connect (bind (&Butler::video, this, _1, _2));
 	_player_audio_connection = _player->Audio.connect (bind (&Butler::audio, this, _1, _2));
 	_player_text_connection = _player->Text.connect (bind (&Butler::text, this, _1, _2, _3));
-	_player_changed_connection = _player->Changed.connect (bind (&Butler::player_changed, this, _2));
+	_player_changed_connection = _player->Changed.connect (bind (&Butler::return_seek, this, _2));
+	_player_not_changed_connection = _player->NotChanged.connect (bind (&Butler::return_seek, this, false));
 	_thread = new boost::thread (bind (&Butler::thread, this));
 #ifdef DCPOMATIC_LINUX
 	pthread_setname_np (_thread->native_handle(), "butler");
@@ -309,7 +310,7 @@ Butler::memory_used () const
 }
 
 void
-Butler::player_changed (bool frequent)
+Butler::return_seek (bool frequent)
 {
 	boost::mutex::scoped_lock lm (_mutex);
 	if (_died || _pending_seek_position || frequent) {
diff --git a/src/lib/butler.h b/src/lib/butler.h
index 5b09f6e5f..56374deeb 100644
--- a/src/lib/butler.h
+++ b/src/lib/butler.h
@@ -56,7 +56,7 @@ private:
 	void text (PlayerText pt, TextType type, DCPTimePeriod period);
 	bool should_run () const;
 	void prepare (boost::weak_ptr<PlayerVideo> video) const;
-	void player_changed (bool frequent);
+	void return_seek (bool frequent);
 	void seek_unlocked (DCPTime position, bool accurate);
 
 	boost::shared_ptr<Player> _player;
@@ -101,4 +101,5 @@ private:
 	boost::signals2::scoped_connection _player_audio_connection;
 	boost::signals2::scoped_connection _player_text_connection;
 	boost::signals2::scoped_connection _player_changed_connection;
+	boost::signals2::scoped_connection _player_not_changed_connection;
 };
diff --git a/src/lib/content.cc b/src/lib/content.cc
index 9b16eff7f..3814956d5 100644
--- a/src/lib/content.cc
+++ b/src/lib/content.cc
@@ -182,7 +182,7 @@ void
 Content::signal_changed (int p)
 {
 	try {
-		emit (boost::bind (boost::ref (Changed), shared_from_this (), p, _change_signals_frequent));
+		emit (boost::bind (boost::ref(Changed), shared_from_this(), p, _change_signals_frequent));
 	} catch (boost::bad_weak_ptr) {
 		/* This must be during construction; never mind */
 	}
@@ -201,16 +201,17 @@ Content::set_position (DCPTime p)
 		audio->modify_position (p);
 	}
 
+	ContentChange cc (this, ContentProperty::POSITION);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		if (p == _position) {
+			cc.abort ();
 			return;
 		}
 
 		_position = p;
 	}
-
-	signal_changed (ContentProperty::POSITION);
 }
 
 void
@@ -226,23 +227,23 @@ Content::set_trim_start (ContentTime t)
 		audio->modify_trim_start (t);
 	}
 
+	ContentChange cc (this, ContentProperty::TRIM_START);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_trim_start = t;
 	}
-
-	signal_changed (ContentProperty::TRIM_START);
 }
 
 void
 Content::set_trim_end (ContentTime t)
 {
+	ContentChange cc (this, ContentProperty::TRIM_END);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_trim_end = t;
 	}
-
-	signal_changed (ContentProperty::TRIM_END);
 }
 
 
@@ -305,16 +306,16 @@ Content::paths_valid () const
 void
 Content::set_path (boost::filesystem::path path)
 {
+	ContentChange cc (this, ContentProperty::PATH);
 	_paths.clear ();
 	_paths.push_back (path);
-	signal_changed (ContentProperty::PATH);
 }
 
 void
 Content::set_paths (vector<boost::filesystem::path> paths)
 {
+	ContentChange cc (this, ContentProperty::PATH);
 	_paths = paths;
-	signal_changed (ContentProperty::PATH);
 }
 
 string
@@ -364,13 +365,13 @@ Content::reel_split_points () const
 void
 Content::set_video_frame_rate (double r)
 {
+	ContentChange cc (this, ContentProperty::VIDEO_FRAME_RATE);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_video_frame_rate = r;
 	}
 
-	signal_changed (ContentProperty::VIDEO_FRAME_RATE);
-
 	/* Make sure things are still on frame boundaries */
 	if (video) {
 		set_position (position());
@@ -381,12 +382,12 @@ Content::set_video_frame_rate (double r)
 void
 Content::unset_video_frame_rate ()
 {
+	ContentChange cc (this, ContentProperty::VIDEO_FRAME_RATE);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_video_frame_rate = optional<double>();
 	}
-
-	signal_changed (ContentProperty::VIDEO_FRAME_RATE);
 }
 
 double
diff --git a/src/lib/content.h b/src/lib/content.h
index 23afa2243..c9edf6e22 100644
--- a/src/lib/content.h
+++ b/src/lib/content.h
@@ -178,8 +178,15 @@ public:
 
 	std::list<UserProperty> user_properties () const;
 
+	/* May be emitted from any thread */
+	boost::signals2::signal<void ()> MayChange;
+
+	/* Emitted from the GUI thread */
 	boost::signals2::signal<void (boost::weak_ptr<Content>, int, bool)> Changed;
 
+	/* May be emitted from any thread */
+	boost::signals2::signal<void ()> NotChanged;
+
 	boost::shared_ptr<VideoContent> video;
 	boost::shared_ptr<AudioContent> audio;
 	std::list<boost::shared_ptr<TextContent> > text;
@@ -187,8 +194,6 @@ public:
 	boost::shared_ptr<TextContent> only_text () const;
 	boost::shared_ptr<TextContent> text_of_original_type (TextType type) const;
 
-	void signal_changed (int);
-
 protected:
 
 	virtual void add_properties (std::list<UserProperty> &) const;
@@ -208,6 +213,9 @@ private:
 	friend struct best_dcp_frame_rate_test_single;
 	friend struct best_dcp_frame_rate_test_double;
 	friend struct audio_sampling_rate_test;
+	friend class ContentChange;
+
+	void signal_changed (int);
 
 	std::string _digest;
 	DCPTime _position;
diff --git a/src/lib/content_part.h b/src/lib/content_part.h
index 4f6e9e396..58833655f 100644
--- a/src/lib/content_part.h
+++ b/src/lib/content_part.h
@@ -23,6 +23,7 @@
 #define DCPOMATIC_CONTENT_PART_H
 
 #include "content.h"
+#include "content_change.h"
 #include <boost/weak_ptr.hpp>
 #include <boost/thread/mutex.hpp>
 
@@ -41,28 +42,30 @@ protected:
 	void
 	maybe_set (T& member, T new_value, int property) const
 	{
+		ContentChange cc (_parent, property);
 		{
 			boost::mutex::scoped_lock lm (_mutex);
 			if (member == new_value) {
+				cc.abort ();
 				return;
 			}
 			member = new_value;
 		}
-		_parent->signal_changed (property);
 	}
 
 	template <class T>
 	void
 	maybe_set (boost::optional<T>& member, T new_value, int property) const
 	{
+		ContentChange cc (_parent, property);
 		{
 			boost::mutex::scoped_lock lm (_mutex);
 			if (member && member.get() == new_value) {
+				cc.abort ();
 				return;
 			}
 			member = new_value;
 		}
-		_parent->signal_changed (property);
 	}
 
 	Content* _parent;
diff --git a/src/lib/dcp_content.cc b/src/lib/dcp_content.cc
index b6a66f90a..a527b1f80 100644
--- a/src/lib/dcp_content.cc
+++ b/src/lib/dcp_content.cc
@@ -61,6 +61,7 @@ int const DCPContentProperty::REFERENCE_AUDIO    = 603;
 int const DCPContentProperty::REFERENCE_TEXT     = 604;
 int const DCPContentProperty::NAME               = 605;
 int const DCPContentProperty::TEXTS              = 606;
+int const DCPContentProperty::CPL                = 607;
 
 DCPContent::DCPContent (shared_ptr<const Film> film, boost::filesystem::path p)
 	: Content (film)
@@ -158,6 +159,12 @@ DCPContent::examine (shared_ptr<Job> job)
 	string const old_name = name ();
 	int const old_texts = text.size ();
 
+	ContentChange cc_texts (this, DCPContentProperty::TEXTS);
+	ContentChange cc_assets (this, DCPContentProperty::NEEDS_ASSETS);
+	ContentChange cc_kdm (this, DCPContentProperty::NEEDS_KDM);
+	ContentChange cc_name (this, DCPContentProperty::NAME);
+	ContentChange cc_streams (this, AudioContentProperty::STREAMS);
+
 	if (job) {
 		job->set_progress_unknown ();
 	}
@@ -175,6 +182,7 @@ DCPContent::examine (shared_ptr<Job> job)
 	}
 
 	if (examiner->has_audio()) {
+		ContentChange cc (this, AudioContentProperty::STREAMS);
 		{
 			boost::mutex::scoped_lock lm (_mutex);
 			audio.reset (new AudioContent (this));
@@ -184,7 +192,6 @@ DCPContent::examine (shared_ptr<Job> job)
 		AudioMapping m = as->mapping ();
 		film()->make_audio_mapping_default (m);
 		as->set_mapping (m);
-		signal_changed (AudioContentProperty::STREAMS);
 	}
 
 	int texts = 0;
@@ -206,24 +213,22 @@ DCPContent::examine (shared_ptr<Job> job)
 		_reel_lengths = examiner->reel_lengths ();
 	}
 
-	if (old_texts != texts) {
-		signal_changed (DCPContentProperty::TEXTS);
+	if (old_texts == texts) {
+		cc_texts.abort ();
 	}
 
-	if (needed_assets != needs_assets ()) {
-		signal_changed (DCPContentProperty::NEEDS_ASSETS);
+	if (needed_assets == needs_assets()) {
+		cc_assets.abort ();
 	}
 
-	if (needed_kdm != needs_kdm ()) {
-		signal_changed (DCPContentProperty::NEEDS_KDM);
+	if (needed_kdm == needs_kdm()) {
+		cc_kdm.abort ();
 	}
 
-	if (old_name != name ()) {
-		signal_changed (DCPContentProperty::NAME);
+	if (old_name == name()) {
+		cc_name.abort ();
 	}
 
-	signal_changed (AudioContentProperty::STREAMS);
-
 	if (video) {
 		video->set_frame_type (_three_d ? VIDEO_FRAME_TYPE_3D : VIDEO_FRAME_TYPE_2D);
 	}
@@ -396,34 +401,34 @@ DCPContent::set_default_colour_conversion ()
 void
 DCPContent::set_reference_video (bool r)
 {
+	ContentChange cc (this, DCPContentProperty::REFERENCE_VIDEO);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_reference_video = r;
 	}
-
-	signal_changed (DCPContentProperty::REFERENCE_VIDEO);
 }
 
 void
 DCPContent::set_reference_audio (bool r)
 {
+	ContentChange cc (this, DCPContentProperty::REFERENCE_AUDIO);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_reference_audio = r;
 	}
-
-	signal_changed (DCPContentProperty::REFERENCE_AUDIO);
 }
 
 void
 DCPContent::set_reference_text (TextType type, bool r)
 {
+	ContentChange cc (this, DCPContentProperty::REFERENCE_TEXT);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_reference_text[type] = r;
 	}
-
-	signal_changed (DCPContentProperty::REFERENCE_TEXT);
 }
 
 list<DCPTimePeriod>
@@ -644,6 +649,10 @@ DCPContent::take_settings_from (shared_ptr<const Content> c)
 void
 DCPContent::set_cpl (string id)
 {
-	boost::mutex::scoped_lock lm (_mutex);
-	_cpl = id;
+	ContentChange cc (this, DCPContentProperty::CPL);
+
+	{
+		boost::mutex::scoped_lock lm (_mutex);
+		_cpl = id;
+	}
 }
diff --git a/src/lib/dcp_content.h b/src/lib/dcp_content.h
index cccf127c3..43476e729 100644
--- a/src/lib/dcp_content.h
+++ b/src/lib/dcp_content.h
@@ -39,6 +39,7 @@ public:
 	static int const REFERENCE_TEXT;
 	static int const NAME;
 	static int const TEXTS;
+	static int const CPL;
 };
 
 class ContentPart;
diff --git a/src/lib/ffmpeg_content.cc b/src/lib/ffmpeg_content.cc
index ebcbcc47e..05b6ae8ea 100644
--- a/src/lib/ffmpeg_content.cc
+++ b/src/lib/ffmpeg_content.cc
@@ -251,6 +251,9 @@ FFmpegContent::as_xml (xmlpp::Node* node, bool with_paths) const
 void
 FFmpegContent::examine (shared_ptr<Job> job)
 {
+	ContentChange cc1 (this, FFmpegContentProperty::SUBTITLE_STREAMS);
+	ContentChange cc2 (this, FFmpegContentProperty::SUBTITLE_STREAM);
+
 	job->set_progress_unknown ();
 
 	Content::examine (job);
@@ -313,9 +316,6 @@ FFmpegContent::examine (shared_ptr<Job> job)
 	if (examiner->has_video ()) {
 		set_default_colour_conversion ();
 	}
-
-	signal_changed (FFmpegContentProperty::SUBTITLE_STREAMS);
-	signal_changed (FFmpegContentProperty::SUBTITLE_STREAM);
 }
 
 string
@@ -369,12 +369,12 @@ FFmpegContent::technical_summary () const
 void
 FFmpegContent::set_subtitle_stream (shared_ptr<FFmpegSubtitleStream> s)
 {
+	ContentChange cc (this, FFmpegContentProperty::SUBTITLE_STREAM);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_subtitle_stream = s;
 	}
-
-	signal_changed (FFmpegContentProperty::SUBTITLE_STREAM);
 }
 
 bool
@@ -410,12 +410,12 @@ FFmpegContent::full_length () const
 void
 FFmpegContent::set_filters (vector<Filter const *> const & filters)
 {
+	ContentChange cc (this, FFmpegContentProperty::FILTERS);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_filters = filters;
 	}
-
-	signal_changed (FFmpegContentProperty::FILTERS);
 }
 
 string
@@ -629,7 +629,8 @@ FFmpegContent::add_properties (list<UserProperty>& p) const
 void
 FFmpegContent::signal_subtitle_stream_changed ()
 {
-	signal_changed (FFmpegContentProperty::SUBTITLE_STREAM);
+	/* XXX: this is too late; really it should be before the change */
+	ContentChange cc (this, FFmpegContentProperty::SUBTITLE_STREAM);
 }
 
 vector<shared_ptr<FFmpegAudioStream> >
diff --git a/src/lib/player.cc b/src/lib/player.cc
index 4ee7d9359..91f1cb517 100644
--- a/src/lib/player.cc
+++ b/src/lib/player.cc
@@ -87,7 +87,7 @@ int const PlayerProperty::DCP_DECODE_REDUCTION = 704;
 Player::Player (shared_ptr<const Film> film, shared_ptr<const Playlist> playlist)
 	: _film (film)
 	, _playlist (playlist)
-	, _have_valid_pieces (false)
+	, _can_run (false)
 	, _ignore_video (false)
 	, _ignore_audio (false)
 	, _ignore_text (false)
@@ -99,11 +99,14 @@ Player::Player (shared_ptr<const Film> film, shared_ptr<const Playlist> playlist
 {
 	_film_changed_connection = _film->Changed.connect (bind (&Player::film_changed, this, _1));
 	_playlist_changed_connection = _playlist->Changed.connect (bind (&Player::playlist_changed, this));
-	_playlist_content_changed_connection = _playlist->ContentChanged.connect (bind (&Player::playlist_content_changed, this, _1, _2, _3));
+	_playlist_content_may_change_connection = _playlist->ContentMayChange.connect (bind(&Player::playlist_content_may_change, this));
+	_playlist_content_changed_connection = _playlist->ContentChanged.connect (bind(&Player::playlist_content_changed, this, _1, _2, _3));
+	_playlist_content_not_changed_connection = _playlist->ContentNotChanged.connect (bind(&Player::playlist_content_not_changed, this));
 	set_video_container_size (_film->frame_size ());
 
 	film_changed (Film::AUDIO_PROCESSOR);
 
+	setup_pieces ();
 	seek (DCPTime (), true);
 }
 
@@ -115,6 +118,13 @@ Player::~Player ()
 void
 Player::setup_pieces ()
 {
+	boost::mutex::scoped_lock lm (_mutex);
+	setup_pieces_unlocked ();
+}
+
+void
+Player::setup_pieces_unlocked ()
+{
 	_pieces.clear ();
 
 	delete _shuffler;
@@ -210,17 +220,38 @@ Player::setup_pieces ()
 	_last_video_time = DCPTime ();
 	_last_video_eyes = EYES_BOTH;
 	_last_audio_time = DCPTime ();
-	_have_valid_pieces = true;
+	_can_run = true;
+}
+
+void
+Player::playlist_content_may_change ()
+{
+	{
+		boost::mutex::scoped_lock lm (_mutex);
+		/* The player content is probably about to change, so we can't carry on
+		   until that has happened and we've rebuilt our pieces.  Stop pass()
+		   and seek() from working until then.
+		*/
+		_can_run = false;
+	}
+
+	MayChange ();
 }
 
 void
 Player::playlist_content_changed (weak_ptr<Content> w, int property, bool frequent)
 {
+	/* A change in our content has gone through.  Re-build our pieces and signal
+	   it to anybody that is interested.
+	*/
+
 	shared_ptr<Content> c = w.lock ();
 	if (!c) {
 		return;
 	}
 
+	setup_pieces ();
+
 	if (
 		property == ContentProperty::POSITION ||
 		property == ContentProperty::LENGTH ||
@@ -232,21 +263,12 @@ Player::playlist_content_changed (weak_ptr<Content> w, int property, bool freque
 		property == AudioContentProperty::STREAMS ||
 		property == DCPContentProperty::NEEDS_ASSETS ||
 		property == DCPContentProperty::NEEDS_KDM ||
+		property == DCPContentProperty::CPL ||
 		property == TextContentProperty::COLOUR ||
 		property == TextContentProperty::EFFECT ||
 		property == TextContentProperty::EFFECT_COLOUR ||
 		property == FFmpegContentProperty::SUBTITLE_STREAM ||
-		property == FFmpegContentProperty::FILTERS
-		) {
-
-		{
-			boost::mutex::scoped_lock lm (_mutex);
-			_have_valid_pieces = false;
-		}
-
-		Changed (property, frequent);
-
-	} else if (
+		property == FFmpegContentProperty::FILTERS ||
 		property == TextContentProperty::LINE_SPACING ||
 		property == TextContentProperty::OUTLINE_WIDTH ||
 		property == TextContentProperty::Y_SCALE ||
@@ -270,6 +292,14 @@ Player::playlist_content_changed (weak_ptr<Content> w, int property, bool freque
 }
 
 void
+Player::playlist_content_not_changed ()
+{
+	/* A possible content change did end up happening for some reason */
+	setup_pieces ();
+	NotChanged ();
+}
+
+void
 Player::set_video_container_size (dcp::Size s)
 {
 	{
@@ -291,11 +321,7 @@ Player::set_video_container_size (dcp::Size s)
 void
 Player::playlist_changed ()
 {
-	{
-		boost::mutex::scoped_lock lm (_mutex);
-		_have_valid_pieces = false;
-	}
-
+	setup_pieces ();
 	Changed (PlayerProperty::PLAYLIST, false);
 }
 
@@ -313,10 +339,7 @@ Player::film_changed (Film::Property p)
 		/* Pieces contain a FrameRateChange which contains the DCP frame rate,
 		   so we need new pieces here.
 		*/
-		{
-			boost::mutex::scoped_lock lm (_mutex);
-			_have_valid_pieces = false;
-		}
+		setup_pieces ();
 		Changed (PlayerProperty::FILM_VIDEO_FRAME_RATE, false);
 	} else if (p == Film::AUDIO_PROCESSOR) {
 		if (_film->audio_processor ()) {
@@ -441,11 +464,7 @@ Player::content_time_to_dcp (shared_ptr<const Piece> piece, ContentTime t) const
 list<shared_ptr<Font> >
 Player::get_subtitle_fonts ()
 {
-	/* Does not require a lock on _mutex as it's only called from DCPEncoder */
-
-	if (!_have_valid_pieces) {
-		setup_pieces ();
-	}
+	boost::mutex::scoped_lock lm (_mutex);
 
 	list<shared_ptr<Font> > fonts;
 	BOOST_FOREACH (shared_ptr<Piece> i, _pieces) {
@@ -467,7 +486,7 @@ Player::set_ignore_video ()
 {
 	boost::mutex::scoped_lock lm (_mutex);
 	_ignore_video = true;
-	setup_pieces ();
+	setup_pieces_unlocked ();
 }
 
 void
@@ -475,7 +494,7 @@ Player::set_ignore_audio ()
 {
 	boost::mutex::scoped_lock lm (_mutex);
 	_ignore_audio = true;
-	setup_pieces ();
+	setup_pieces_unlocked ();
 }
 
 void
@@ -483,7 +502,7 @@ Player::set_ignore_text ()
 {
 	boost::mutex::scoped_lock lm (_mutex);
 	_ignore_text = true;
-	setup_pieces ();
+	setup_pieces_unlocked ();
 }
 
 /** Set the player to always burn open texts into the image regardless of the content settings */
@@ -500,7 +519,7 @@ Player::set_fast ()
 {
 	boost::mutex::scoped_lock lm (_mutex);
 	_fast = true;
-	setup_pieces ();
+	setup_pieces_unlocked ();
 }
 
 void
@@ -508,7 +527,7 @@ Player::set_play_referenced ()
 {
 	boost::mutex::scoped_lock lm (_mutex);
 	_play_referenced = true;
-	setup_pieces ();
+	setup_pieces_unlocked ();
 }
 
 list<ReferencedReelAsset>
@@ -594,13 +613,8 @@ Player::pass ()
 {
 	boost::mutex::scoped_lock lm (_mutex);
 
-	if (!_have_valid_pieces) {
-		/* This should only happen when we are under the control of the butler.  In this case, _have_valid_pieces
-		   will be false if something in the Player has changed and we are waiting for the butler to notice
-		   and do a seek back to the place we were at before.  During this time we don't want pass() to do anything,
-		   as just after setup_pieces the new decoders will be back to time 0 until the seek has gone through.  Just do nothing
-		   here and assume that the seek will be forthcoming.
-		*/
+	if (!_can_run) {
+		/* We can't pass in this state */
 		return false;
 	}
 
@@ -1025,8 +1039,9 @@ Player::seek (DCPTime time, bool accurate)
 {
 	boost::mutex::scoped_lock lm (_mutex);
 
-	if (!_have_valid_pieces) {
-		setup_pieces ();
+	if (!_can_run) {
+		/* We can't seek in this state */
+		return;
 	}
 
 	if (_shuffler) {
@@ -1181,27 +1196,23 @@ Player::set_dcp_decode_reduction (optional<int> reduction)
 		}
 
 		_dcp_decode_reduction = reduction;
-		_have_valid_pieces = false;
+		setup_pieces_unlocked ();
 	}
 
 	Changed (PlayerProperty::DCP_DECODE_REDUCTION, false);
 }
 
-DCPTime
+optional<DCPTime>
 Player::content_time_to_dcp (shared_ptr<Content> content, ContentTime t)
 {
 	boost::mutex::scoped_lock lm (_mutex);
 
-	if (_have_valid_pieces) {
-		setup_pieces ();
-	}
-
 	BOOST_FOREACH (shared_ptr<Piece> i, _pieces) {
 		if (i->content == content) {
 			return content_time_to_dcp (i, t);
 		}
 	}
 
-	DCPOMATIC_ASSERT (false);
-	return DCPTime ();
+	/* We couldn't find this content; perhaps things are being changed over */
+	return optional<DCPTime>();
 }
diff --git a/src/lib/player.h b/src/lib/player.h
index 20b68ef77..c43cfd40e 100644
--- a/src/lib/player.h
+++ b/src/lib/player.h
@@ -86,7 +86,9 @@ public:
 	void set_play_referenced ();
 	void set_dcp_decode_reduction (boost::optional<int> reduction);
 
-	DCPTime content_time_to_dcp (boost::shared_ptr<Content> content, ContentTime t);
+	boost::optional<DCPTime> content_time_to_dcp (boost::shared_ptr<Content> content, ContentTime t);
+
+	boost::signals2::signal<void ()> MayChange;
 
 	/** Emitted when something has changed such that if we went back and emitted
 	 *  the last frame again it would look different.  This is not emitted after
@@ -96,6 +98,7 @@ public:
 	 *  The second parameter is true if these signals are currently likely to be frequent.
 	 */
 	boost::signals2::signal<void (int, bool)> Changed;
+	boost::signals2::signal<void ()> NotChanged;
 
 	/** Emitted when a video frame is ready.  These emissions happen in the correct order. */
 	boost::signals2::signal<void (boost::shared_ptr<PlayerVideo>, DCPTime)> Video;
@@ -114,10 +117,13 @@ private:
 	friend struct player_subframe_test;
 
 	void setup_pieces ();
+	void setup_pieces_unlocked ();
 	void flush ();
 	void film_changed (Film::Property);
 	void playlist_changed ();
+	void playlist_content_may_change ();
 	void playlist_content_changed (boost::weak_ptr<Content>, int, bool);
+	void playlist_content_not_changed ();
 	std::list<PositionImage> transform_bitmap_texts (std::list<BitmapText>) const;
 	Frame dcp_to_content_video (boost::shared_ptr<const Piece> piece, DCPTime t) const;
 	DCPTime content_video_to_dcp (boost::shared_ptr<const Piece> piece, Frame f) const;
@@ -150,8 +156,8 @@ private:
 	boost::shared_ptr<const Film> _film;
 	boost::shared_ptr<const Playlist> _playlist;
 
-	/** Our pieces are ready to go; if this is false the pieces must be (re-)created before they are used */
-	bool _have_valid_pieces;
+	/** We can pass() and seek() */
+	bool _can_run;
 	std::list<boost::shared_ptr<Piece> > _pieces;
 
 	/** Size of the image in the DCP (e.g. 1990x1080 for flat) */
@@ -207,7 +213,9 @@ private:
 
 	boost::signals2::scoped_connection _film_changed_connection;
 	boost::signals2::scoped_connection _playlist_changed_connection;
+	boost::signals2::scoped_connection _playlist_content_may_change_connection;
 	boost::signals2::scoped_connection _playlist_content_changed_connection;
+	boost::signals2::scoped_connection _playlist_content_not_changed_connection;
 };
 
 #endif
diff --git a/src/lib/playlist.cc b/src/lib/playlist.cc
index c830e5e1e..1bb0ad0d6 100644
--- a/src/lib/playlist.cc
+++ b/src/lib/playlist.cc
@@ -65,6 +65,18 @@ Playlist::~Playlist ()
 }
 
 void
+Playlist::content_may_change ()
+{
+	ContentMayChange ();
+}
+
+void
+Playlist::content_not_changed ()
+{
+	ContentNotChanged ();
+}
+
+void
 Playlist::content_changed (weak_ptr<Content> content, int property, bool frequent)
 {
 	if (
@@ -350,7 +362,9 @@ Playlist::reconnect ()
 	_content_connections.clear ();
 
 	BOOST_FOREACH (shared_ptr<Content> i, _content) {
-		_content_connections.push_back (i->Changed.connect (bind (&Playlist::content_changed, this, _1, _2, _3)));
+		_content_connections.push_back (i->MayChange.connect(boost::bind(&Playlist::content_may_change, this)));
+		_content_connections.push_back (i->Changed.connect(boost::bind(&Playlist::content_changed, this, _1, _2, _3)));
+		_content_connections.push_back (i->NotChanged.connect(boost::bind(&Playlist::content_not_changed, this)));
 	}
 }
 
diff --git a/src/lib/playlist.h b/src/lib/playlist.h
index 4ee120198..649887f72 100644
--- a/src/lib/playlist.h
+++ b/src/lib/playlist.h
@@ -77,14 +77,19 @@ public:
 	/** Emitted when content has been added to or removed from the playlist; implies OrderChanged */
 	mutable boost::signals2::signal<void ()> Changed;
 	mutable boost::signals2::signal<void ()> OrderChanged;
+
+	mutable boost::signals2::signal<void ()> ContentMayChange;
 	/** Emitted when something about a piece of our content has changed;
 	 *  these emissions include when the position of the content changes.
 	 *  Third parameter is true if signals are currently being emitted frequently.
 	 */
 	mutable boost::signals2::signal<void (boost::weak_ptr<Content>, int, bool)> ContentChanged;
+	mutable boost::signals2::signal<void ()> ContentNotChanged;
 
 private:
+	void content_may_change ();
 	void content_changed (boost::weak_ptr<Content>, int, bool);
+	void content_not_changed ();
 	void reconnect ();
 
 	/** List of content.  Kept sorted in position order. */
diff --git a/src/lib/text_content.cc b/src/lib/text_content.cc
index ee29ae8c4..35dee525a 100644
--- a/src/lib/text_content.cc
+++ b/src/lib/text_content.cc
@@ -426,7 +426,8 @@ TextContent::connect_to_fonts ()
 void
 TextContent::font_changed ()
 {
-	_parent->signal_changed (TextContentProperty::FONTS);
+	/* XXX: too late */
+	ContentChange cc (_parent, TextContentProperty::FONTS);
 }
 
 void
diff --git a/src/lib/video_content.cc b/src/lib/video_content.cc
index d3ba6c1ab..81f4138fb 100644
--- a/src/lib/video_content.cc
+++ b/src/lib/video_content.cc
@@ -234,6 +234,10 @@ VideoContent::take_from_examiner (shared_ptr<VideoExaminer> d)
 	optional<double> const ar = d->sample_aspect_ratio ();
 	bool const yuv = d->yuv ();
 
+	ContentChange cc1 (_parent, VideoContentProperty::SIZE);
+	ContentChange cc2 (_parent, VideoContentProperty::SCALE);
+	ContentChange cc3 (_parent, ContentProperty::LENGTH);
+
 	{
 		boost::mutex::scoped_lock lm (_mutex);
 		_size = vs;
@@ -256,10 +260,6 @@ VideoContent::take_from_examiner (shared_ptr<VideoExaminer> d)
 	if (d->video_frame_rate()) {
 		_parent->set_video_frame_rate (d->video_frame_rate().get());
 	}
-
-	_parent->signal_changed (VideoContentProperty::SIZE);
-	_parent->signal_changed (VideoContentProperty::SCALE);
-	_parent->signal_changed (ContentProperty::LENGTH);
 }
 
 /** @return string which includes everything about how this content looks */
diff --git a/src/lib/wscript b/src/lib/wscript
index 0cc3d7823..68e44ccd0 100644
--- a/src/lib/wscript
+++ b/src/lib/wscript
@@ -47,6 +47,7 @@ sources = """
           colour_conversion.cc
           config.cc
           content.cc
+          content_change.cc
           content_factory.cc
           cross.cc
           curl_uploader.cc
diff --git a/src/wx/film_viewer.cc b/src/wx/film_viewer.cc
index d00c0bfaf..0e0fc4315 100644
--- a/src/wx/film_viewer.cc
+++ b/src/wx/film_viewer.cc
@@ -767,7 +767,10 @@ FilmViewer::set_position (DCPTime p)
 void
 FilmViewer::set_position (shared_ptr<Content> content, ContentTime t)
 {
-	set_position (_player->content_time_to_dcp (content, t));
+	optional<DCPTime> dt = _player->content_time_to_dcp (content, t);
+	if (dt) {
+		set_position (*dt);
+	}
 }
 
 void