Fix problems with subtitles when there is a non-zero PTS offset

in FFmpegDecoder.  This offset was not being taken into account for
subtitles prior to this commit.

6 files changed, 86 insertions, 45 deletions

diff --git a/src/lib/ffmpeg.cc b/src/lib/ffmpeg.cc
index 8fa03fdff..de08e9df9 100644
--- a/src/lib/ffmpeg.cc
+++ b/src/lib/ffmpeg.cc
@@ -25,6 +25,7 @@
 #include "raw_convert.h"
 #include "log.h"
 #include "ffmpeg_subtitle_stream.h"
+#include "ffmpeg_audio_stream.h"
 #include "compose.hpp"
 extern "C" {
 #include <libavcodec/avcodec.h>
@@ -32,6 +33,7 @@ extern "C" {
 #include <libswscale/swscale.h>
 }
 #include <boost/algorithm/string.hpp>
+#include <boost/foreach.hpp>
 #include <iostream>
 
 #include "i18n.h"
@@ -39,7 +41,9 @@ extern "C" {
 using std::string;
 using std::cout;
 using std::cerr;
+using std::vector;
 using boost::shared_ptr;
+using boost::optional;
 
 boost::mutex FFmpeg::_mutex;
 boost::weak_ptr<Log> FFmpeg::_ffmpeg_log;
@@ -263,3 +267,55 @@ FFmpeg::subtitle_period (AVSubtitle const & sub)
 		packet_time + ContentTime::from_seconds (sub.end_display_time / 1e3)
 		);
 }
+
+/** Compute the pts offset to use given a set of audio streams and some video details.
+ *  Sometimes these parameters will have just been determined by an Examiner, sometimes
+ *  they will have been retrieved from a piece of Content, hence the need for this method
+ *  in FFmpeg.
+ */
+ContentTime
+FFmpeg::pts_offset (vector<shared_ptr<FFmpegAudioStream> > audio_streams, optional<ContentTime> first_video, double video_frame_rate) const
+{
+	/* Audio and video frame PTS values may not start with 0.  We want
+	   to fiddle them so that:
+
+	   1.  One of them starts at time 0.
+	   2.  The first video PTS value ends up on a frame boundary.
+
+	   Then we remove big initial gaps in PTS and we allow our
+	   insertion of black frames to work.
+
+	   We will do:
+	     audio_pts_to_use = audio_pts_from_ffmpeg + pts_offset;
+	     video_pts_to_use = video_pts_from_ffmpeg + pts_offset;
+	*/
+
+	/* First, make one of them start at 0 */
+
+	ContentTime po = ContentTime::min ();
+
+	if (first_video) {
+		po = - first_video.get ();
+	}
+
+	BOOST_FOREACH (shared_ptr<FFmpegAudioStream> i, audio_streams) {
+		if (i->first_audio) {
+			po = max (po, - i->first_audio.get ());
+		}
+	}
+
+	/* If the offset is positive we would be pushing things from a -ve PTS to be played.
+	   I don't think we ever want to do that, as it seems things at -ve PTS are not meant
+	   to be seen (use for alignment bars etc.); see mantis #418.
+	*/
+	if (po > ContentTime ()) {
+		po = ContentTime ();
+	}
+
+	/* Now adjust so that the video pts starts on a frame */
+	if (first_video) {
+		po += first_video.get().round_up (video_frame_rate) - first_video.get();
+	}
+
+	return po;
+}
diff --git a/src/lib/ffmpeg.h b/src/lib/ffmpeg.h
index 961f5cbb1..b3bc13e5c 100644
--- a/src/lib/ffmpeg.h
+++ b/src/lib/ffmpeg.h
@@ -33,6 +33,7 @@ struct AVFrame;
 struct AVIOContext;
 
 class FFmpegContent;
+class FFmpegAudioStream;
 class Log;
 
 class FFmpeg
@@ -51,6 +52,10 @@ public:
 protected:
 	AVCodecContext* video_codec_context () const;
 	AVCodecContext* subtitle_codec_context () const;
+	ContentTime pts_offset (
+		std::vector<boost::shared_ptr<FFmpegAudioStream> > audio_streams, boost::optional<ContentTime> first_video, double video_frame_rate
+		) const;
+
 	static FFmpegSubtitlePeriod subtitle_period (AVSubtitle const &);
 
 	boost::shared_ptr<const FFmpegContent> _ffmpeg_content;
diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index d343ec317..475418d3d 100644
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -67,51 +67,9 @@ FFmpegDecoder::FFmpegDecoder (shared_ptr<const FFmpegContent> c, shared_ptr<Log>
 	, SubtitleDecoder (c)
 	, FFmpeg (c)
 	, _log (log)
+	, _pts_offset (pts_offset (c->ffmpeg_audio_streams(), c->first_video(), c->video_frame_rate()))
 {
-	/* Audio and video frame PTS values may not start with 0.  We want
-	   to fiddle them so that:
 
-	   1.  One of them starts at time 0.
-	   2.  The first video PTS value ends up on a frame boundary.
-
-	   Then we remove big initial gaps in PTS and we allow our
-	   insertion of black frames to work.
-
-	   We will do:
-	     audio_pts_to_use = audio_pts_from_ffmpeg + pts_offset;
-	     video_pts_to_use = video_pts_from_ffmpeg + pts_offset;
-	*/
-
-	/* First, make one of them start at 0 */
-
-	vector<shared_ptr<FFmpegAudioStream> > streams = c->ffmpeg_audio_streams ();
-
-	_pts_offset = ContentTime::min ();
-
-	if (c->first_video ()) {
-		_pts_offset = - c->first_video().get ();
-	}
-
-	BOOST_FOREACH (shared_ptr<FFmpegAudioStream> i, streams) {
-		if (i->first_audio) {
-			_pts_offset = max (_pts_offset, - i->first_audio.get ());
-		}
-	}
-
-	/* If _pts_offset is positive we would be pushing things from a -ve PTS to be played.
-	   I don't think we ever want to do that, as it seems things at -ve PTS are not meant
-	   to be seen (use for alignment bars etc.); see mantis #418.
-	*/
-	if (_pts_offset > ContentTime ()) {
-		_pts_offset = ContentTime ();
-	}
-
-	/* Now adjust so that the video pts starts on a frame */
-	if (c->first_video ()) {
-		ContentTime first_video = c->first_video().get() + _pts_offset;
-		ContentTime const old_first_video = first_video;
-		_pts_offset += first_video.round_up (c->video_frame_rate ()) - old_first_video;
-	}
 }
 
 void
@@ -457,7 +415,7 @@ FFmpegDecoder::decode_subtitle_packet ()
 		period.to = sub_period.to.get() + _pts_offset;
 	} else {
 		/* We have to look up the `to' time in the stream's records */
-		period.to = ffmpeg_content()->subtitle_stream()->find_subtitle_to (sub_period.from);
+		period.to = ffmpeg_content()->subtitle_stream()->find_subtitle_to (period.from);
 	}
 
 	AVSubtitleRect const * rect = sub.rects[0];
diff --git a/src/lib/ffmpeg_examiner.cc b/src/lib/ffmpeg_examiner.cc
index 6173e0415..40fe0d28e 100644
--- a/src/lib/ffmpeg_examiner.cc
+++ b/src/lib/ffmpeg_examiner.cc
@@ -30,6 +30,7 @@ extern "C" {
 #include "ffmpeg_subtitle_stream.h"
 #include "util.h"
 #include "safe_stringstream.h"
+#include <boost/foreach.hpp>
 #include <iostream>
 
 #include "i18n.h"
@@ -145,6 +146,16 @@ FFmpegExaminer::FFmpegExaminer (shared_ptr<const FFmpegContent> c, shared_ptr<Jo
 				);
 		}
 	}
+
+	/* We just added subtitles to our streams without taking the PTS offset into account;
+	   this is because we might not know the PTS offset when the first subtitle is seen.
+	   Now we know the PTS offset so we can apply it to those subtitles.
+	*/
+	if (video_frame_rate()) {
+		BOOST_FOREACH (shared_ptr<FFmpegSubtitleStream> i, _subtitle_streams) {
+			i->add_offset (pts_offset (_audio_streams, _first_video, video_frame_rate().get()));
+		}
+	}
 }
 
 void
diff --git a/src/lib/ffmpeg_subtitle_stream.cc b/src/lib/ffmpeg_subtitle_stream.cc
index 27099b0f3..e12075581 100644
--- a/src/lib/ffmpeg_subtitle_stream.cc
+++ b/src/lib/ffmpeg_subtitle_stream.cc
@@ -86,3 +86,14 @@ FFmpegSubtitleStream::find_subtitle_to (ContentTime from) const
 	DCPOMATIC_ASSERT (i != _subtitles.end ());
 	return i->second;
 }
+
+/** Add some offset to all the times in the stream */
+void
+FFmpegSubtitleStream::add_offset (ContentTime offset)
+{
+	map<ContentTime, ContentTime> fixed;
+	for (map<ContentTime, ContentTime>::iterator i = _subtitles.begin(); i != _subtitles.end(); ++i) {
+		fixed[i->first + offset] = i->second + offset;
+	}
+	_subtitles = fixed;
+}
diff --git a/src/lib/ffmpeg_subtitle_stream.h b/src/lib/ffmpeg_subtitle_stream.h
index a39b10ffd..0809b359a 100644
--- a/src/lib/ffmpeg_subtitle_stream.h
+++ b/src/lib/ffmpeg_subtitle_stream.h
@@ -34,8 +34,8 @@ public:
 	void add_subtitle (ContentTimePeriod period);
 	std::list<ContentTimePeriod> subtitles_during (ContentTimePeriod period, bool starting) const;
 	ContentTime find_subtitle_to (ContentTime from) const;
+	void add_offset (ContentTime offset);
 
 private:
 	std::map<ContentTime, ContentTime> _subtitles;
 };
-