Improve FFmpeg sync, in theory.

[dcpomatic.git] / src / lib / ffmpeg_decoder.cc

diff --git a/src/lib/ffmpeg_decoder.cc b/src/lib/ffmpeg_decoder.cc
index 1d8a00866e0627fa82dc583cd664e02573335b83..2d1792390dbdbb2e743124d5b6d0c8d87c832afd 100644 (file)
--- a/src/lib/ffmpeg_decoder.cc
+++ b/src/lib/ffmpeg_decoder.cc
@@ -66,8 +66,30 @@ FFmpegDecoder::FFmpegDecoder (shared_ptr<const Film> f, shared_ptr<const FFmpegC
        , _subtitle_codec (0)
        , _decode_video (video)
        , _decode_audio (audio)
+       , _pts_offset (0)
 {
        setup_subtitle ();
+
+       if (video && audio && c->audio_stream() && c->first_video() && c->audio_stream()->first_audio) {
+               _pts_offset = compute_pts_offset (c->first_video().get(), c->audio_stream()->first_audio.get(), c->video_frame_rate());
+       }
+}
+
+double
+FFmpegDecoder::compute_pts_offset (double first_video, double first_audio, float video_frame_rate)
+{
+       assert (first_video >= 0);
+       assert (first_audio >= 0);
+       
+       double const old_first_video = first_video;
+       
+       /* Round the first video to a frame boundary */
+       if (fabs (rint (first_video * video_frame_rate) - first_video * video_frame_rate) > 1e-6) {
+               first_video = ceil (first_video * video_frame_rate) / video_frame_rate;
+       }
+
+       /* Compute the required offset (also removing any common start delay) */
+       return first_video - old_first_video - min (first_video, first_audio);
 }
 
 FFmpegDecoder::~FFmpegDecoder ()
@@ -108,8 +130,8 @@ FFmpegDecoder::pass ()
                }
 
                /* Stop us being asked for any more data */
-               _next_video_frame = _ffmpeg_content->video_length ();
-               _next_audio_frame = _ffmpeg_content->audio_length ();
+               _video_position = _ffmpeg_content->video_length ();
+               _audio_position = _ffmpeg_content->audio_length ();
                return;
        }
 
@@ -267,11 +289,11 @@ FFmpegDecoder::seek (VideoContent::Frame frame)
 void
 FFmpegDecoder::seek_back ()
 {
-       if (_next_video_frame == 0) {
+       if (_video_position == 0) {
                return;
        }
        
-       do_seek (_next_video_frame - 1, true, true);
+       do_seek (_video_position - 1, true, true);
 }
 
 void
@@ -327,17 +349,33 @@ FFmpegDecoder::decode_audio_packet ()
                int const decode_result = avcodec_decode_audio4 (audio_codec_context(), _frame, &frame_finished, &copy_packet);
                if (decode_result >= 0) {
                        if (frame_finished) {
-                       
-                               /* Where we are in the source, in seconds */
-                               double const source_pts_seconds = av_q2d (_format_context->streams[copy_packet.stream_index]->time_base)
-                                       * av_frame_get_best_effort_timestamp(_frame);
+
+                               if (_audio_position == 0) {
+                                       /* Where we are in the source, in seconds */
+                                       double const pts = av_q2d (_format_context->streams[copy_packet.stream_index]->time_base)
+                                               * av_frame_get_best_effort_timestamp(_frame) - _pts_offset;
+
+                                       if (pts > 0) {
+                                               /* Emit some silence */
+                                               shared_ptr<AudioBuffers> silence (
+                                                       new AudioBuffers (
+                                                               _ffmpeg_content->audio_channels(),
+                                                               pts * _ffmpeg_content->content_audio_frame_rate()
+                                                               )
+                                                       );
+                                               
+                                               silence->make_silent ();
+                                               audio (silence, _audio_position);
+                                       }
+                               }
+                                       
                                
                                int const data_size = av_samples_get_buffer_size (
                                        0, audio_codec_context()->channels, _frame->nb_samples, audio_sample_format (), 1
                                        );
                                
                                assert (audio_codec_context()->channels == _ffmpeg_content->audio_channels());
-                               Audio (deinterleave_audio (_frame->data, data_size), source_pts_seconds * _ffmpeg_content->content_audio_frame_rate());
+                               audio (deinterleave_audio (_frame->data, data_size), _audio_position);
                        }
                        
                        copy_packet.data += decode_result;
@@ -389,8 +427,8 @@ FFmpegDecoder::decode_video_packet ()
                int64_t const bet = av_frame_get_best_effort_timestamp (_frame);
                if (bet != AV_NOPTS_VALUE) {
 
-                       double const pts = bet * av_q2d (_format_context->streams[_video_stream]->time_base);
-                       double const next = _next_video_frame / _ffmpeg_content->video_frame_rate();
+                       double const pts = bet * av_q2d (_format_context->streams[_video_stream]->time_base) - _pts_offset;
+                       double const next = _video_position / _ffmpeg_content->video_frame_rate();
                        double const one_frame = 1 / _ffmpeg_content->video_frame_rate ();
                        double delta = pts - next;
 
@@ -407,13 +445,13 @@ FFmpegDecoder::decode_video_packet ()
                                        );
                                
                                black->make_black ();
-                               video (image, false, _next_video_frame);
+                               video (image, false, _video_position);
                                delta -= one_frame;
                        }
 
                        if (delta > -one_frame) {
                                /* This PTS is within a frame of being right; emit this (otherwise it will be dropped) */
-                               video (image, false, _next_video_frame);
+                               video (image, false, _video_position);
                        }
                } else {
                        shared_ptr<const Film> film = _film.lock ();
@@ -450,8 +488,8 @@ FFmpegDecoder::setup_subtitle ()
 bool
 FFmpegDecoder::done () const
 {
-       bool const vd = !_decode_video || (_next_video_frame >= _ffmpeg_content->video_length());
-       bool const ad = !_decode_audio || !_ffmpeg_content->audio_stream() || (_next_audio_frame >= _ffmpeg_content->audio_length());
+       bool const vd = !_decode_video || (_video_position >= _ffmpeg_content->video_length());
+       bool const ad = !_decode_audio || !_ffmpeg_content->audio_stream() || (_audio_position >= _ffmpeg_content->audio_length());
        return vd && ad;
 }