Various fixes to PTS mangling.
[dcpomatic.git] / src / lib / ffmpeg_decoder.cc
index 7b56a59712641cd9de903746f1b9b1a590cf1cea..201fac8aa5a74dabd82ee4e3b577de4b9e239cd1 100644 (file)
 #include <iostream>
 #include <stdint.h>
 #include <boost/lexical_cast.hpp>
+#include <sndfile.h>
 extern "C" {
-#include <tiffio.h>
 #include <libavcodec/avcodec.h>
 #include <libavformat/avformat.h>
-#include <libswscale/swscale.h>
-#include <libpostproc/postprocess.h>
 }
-#include <sndfile.h>
 #include "film.h"
-#include "format.h"
-#include "transcoder.h"
-#include "job.h"
 #include "filter.h"
 #include "exceptions.h"
 #include "image.h"
@@ -47,7 +41,7 @@ extern "C" {
 #include "log.h"
 #include "ffmpeg_decoder.h"
 #include "filter_graph.h"
-#include "subtitle.h"
+#include "audio_buffers.h"
 
 #include "i18n.h"
 
@@ -56,241 +50,125 @@ using std::string;
 using std::vector;
 using std::stringstream;
 using std::list;
+using std::min;
+using std::pair;
 using boost::shared_ptr;
 using boost::optional;
 using boost::dynamic_pointer_cast;
 using libdcp::Size;
 
-FFmpegDecoder::FFmpegDecoder (shared_ptr<const Film> f, shared_ptr<FFmpegContent> c, bool video, bool audio, bool subtitles, bool video_sync)
+FFmpegDecoder::FFmpegDecoder (shared_ptr<const Film> f, shared_ptr<const FFmpegContent> c, bool video, bool audio)
        : Decoder (f)
-       , VideoDecoder (f, c)
-       , AudioDecoder (f, c)
-       , _ffmpeg_content (c)
-       , _format_context (0)
-       , _video_stream (-1)
-       , _frame (0)
-       , _video_codec_context (0)
-       , _video_codec (0)
-       , _audio_codec_context (0)
-       , _audio_codec (0)
+       , VideoDecoder (f)
+       , AudioDecoder (f)
+       , SubtitleDecoder (f)
+       , FFmpeg (c)
        , _subtitle_codec_context (0)
        , _subtitle_codec (0)
        , _decode_video (video)
        , _decode_audio (audio)
-       , _decode_subtitles (subtitles)
-       , _video_sync (video_sync)
+       , _video_pts_offset (0)
+       , _audio_pts_offset (0)
+       , _just_sought (false)
 {
-       setup_general ();
-       setup_video ();
-       setup_audio ();
        setup_subtitle ();
 
-       if (!video_sync) {
-               _first_video = 0;
-       }
-}
+       /* Audio and video frame PTS values may not start with 0.  We want
+          to fiddle them so that:
 
-FFmpegDecoder::~FFmpegDecoder ()
-{
-       if (_audio_codec_context) {
-               avcodec_close (_audio_codec_context);
-       }
-       
-       if (_video_codec_context) {
-               avcodec_close (_video_codec_context);
-       }
+          1.  One of them starts at time 0.
+          2.  The first video PTS value ends up on a frame boundary.
 
-       if (_subtitle_codec_context) {
-               avcodec_close (_subtitle_codec_context);
-       }
+          Then we remove big initial gaps in PTS and we allow our
+          insertion of black frames to work.
 
-       av_free (_frame);
-       
-       avformat_close_input (&_format_context);
-}      
+          We will do:
+            audio_pts_to_use = audio_pts_from_ffmpeg + audio_pts_offset;
+            video_pts_to_use = video_pts_from_ffmpeg + video_pts_offset;
+       */
 
-void
-FFmpegDecoder::setup_general ()
-{
-       av_register_all ();
+       bool const have_video = video && c->first_video();
+       bool const have_audio = audio && c->audio_stream() && c->audio_stream()->first_audio;
 
-       if (avformat_open_input (&_format_context, _ffmpeg_content->file().string().c_str(), 0, 0) < 0) {
-               throw OpenFileError (_ffmpeg_content->file().string ());
-       }
+       /* First, make one of them start at 0 */
 
-       if (avformat_find_stream_info (_format_context, 0) < 0) {
-               throw DecodeError (_("could not find stream information"));
+       if (have_audio && have_video) {
+               _video_pts_offset = _audio_pts_offset = - min (c->first_video().get(), c->audio_stream()->first_audio.get());
+       } else if (have_video) {
+               _video_pts_offset = - c->first_video().get();
        }
 
-       /* Find video, audio and subtitle streams and choose the first of each */
-
-       for (uint32_t i = 0; i < _format_context->nb_streams; ++i) {
-               AVStream* s = _format_context->streams[i];
-               if (s->codec->codec_type == AVMEDIA_TYPE_VIDEO) {
-                       _video_stream = i;
-               } else if (s->codec->codec_type == AVMEDIA_TYPE_AUDIO) {
-
-                       /* This is a hack; sometimes it seems that _audio_codec_context->channel_layout isn't set up,
-                          so bodge it here.  No idea why we should have to do this.
-                       */
-
-                       if (s->codec->channel_layout == 0) {
-                               s->codec->channel_layout = av_get_default_channel_layout (s->codec->channels);
-                       }
-                       
-                       _audio_streams.push_back (
-                               FFmpegAudioStream (stream_name (s), i, s->codec->sample_rate, s->codec->channel_layout)
-                               );
-                       
-               } else if (s->codec->codec_type == AVMEDIA_TYPE_SUBTITLE) {
-                       _subtitle_streams.push_back (FFmpegSubtitleStream (stream_name (s), i));
+       /* Now adjust both so that the video pts starts on a frame */
+       if (have_video && have_audio) {
+               double first_video = c->first_video().get() + _video_pts_offset;
+               double const old_first_video = first_video;
+               
+               /* Round the first video up to a frame boundary */
+               if (fabs (rint (first_video * c->video_frame_rate()) - first_video * c->video_frame_rate()) > 1e-6) {
+                       first_video = ceil (first_video * c->video_frame_rate()) / c->video_frame_rate ();
                }
-       }
-
-       if (_video_stream < 0) {
-               throw DecodeError (N_("could not find video stream"));
-       }
-
-       _frame = avcodec_alloc_frame ();
-       if (_frame == 0) {
-               throw DecodeError (N_("could not allocate frame"));
-       }
-}
-
-void
-FFmpegDecoder::setup_video ()
-{
-       _video_codec_context = _format_context->streams[_video_stream]->codec;
-       _video_codec = avcodec_find_decoder (_video_codec_context->codec_id);
-
-       if (_video_codec == 0) {
-               throw DecodeError (_("could not find video decoder"));
-       }
 
-       if (avcodec_open2 (_video_codec_context, _video_codec, 0) < 0) {
-               throw DecodeError (N_("could not open video decoder"));
+               _video_pts_offset += first_video - old_first_video;
+               _audio_pts_offset += first_video - old_first_video;
        }
 }
 
-void
-FFmpegDecoder::setup_audio ()
+FFmpegDecoder::~FFmpegDecoder ()
 {
-       if (!_ffmpeg_content->audio_stream ()) {
-               return;
-       }
+       boost::mutex::scoped_lock lm (_mutex);
 
-       _audio_codec_context = _format_context->streams[_ffmpeg_content->audio_stream()->id]->codec;
-       _audio_codec = avcodec_find_decoder (_audio_codec_context->codec_id);
-
-       if (_audio_codec == 0) {
-               throw DecodeError (_("could not find audio decoder"));
-       }
-
-       if (avcodec_open2 (_audio_codec_context, _audio_codec, 0) < 0) {
-               throw DecodeError (N_("could not open audio decoder"));
+       if (_subtitle_codec_context) {
+               avcodec_close (_subtitle_codec_context);
        }
-}
+}      
 
 void
-FFmpegDecoder::setup_subtitle ()
-{
-       if (!_ffmpeg_content->subtitle_stream() || _ffmpeg_content->subtitle_stream()->id >= int (_format_context->nb_streams)) {
-               return;
-       }
-
-       _subtitle_codec_context = _format_context->streams[_ffmpeg_content->subtitle_stream()->id]->codec;
-       _subtitle_codec = avcodec_find_decoder (_subtitle_codec_context->codec_id);
-
-       if (_subtitle_codec == 0) {
-               throw DecodeError (_("could not find subtitle decoder"));
-       }
-       
-       if (avcodec_open2 (_subtitle_codec_context, _subtitle_codec, 0) < 0) {
-               throw DecodeError (N_("could not open subtitle decoder"));
-       }
-}
-
-
-bool
 FFmpegDecoder::pass ()
 {
        int r = av_read_frame (_format_context, &_packet);
-       
+
        if (r < 0) {
                if (r != AVERROR_EOF) {
                        /* Maybe we should fail here, but for now we'll just finish off instead */
                        char buf[256];
                        av_strerror (r, buf, sizeof(buf));
-                       _film->log()->log (String::compose (N_("error on av_read_frame (%1) (%2)"), buf, r));
+                       shared_ptr<const Film> film = _film.lock ();
+                       assert (film);
+                       film->log()->log (String::compose (N_("error on av_read_frame (%1) (%2)"), buf, r));
                }
-               
+
                /* Get any remaining frames */
                
                _packet.data = 0;
                _packet.size = 0;
-
+               
                /* XXX: should we reset _packet.data and size after each *_decode_* call? */
-
-               int frame_finished;
-
+               
                if (_decode_video) {
-                       while (avcodec_decode_video2 (_video_codec_context, _frame, &frame_finished, &_packet) >= 0 && frame_finished) {
-                               filter_and_emit_video (_frame);
-                       }
+                       while (decode_video_packet ()) {}
                }
 
                if (_ffmpeg_content->audio_stream() && _decode_audio) {
                        decode_audio_packet ();
                }
 
-               return true;
+               /* Stop us being asked for any more data */
+               _video_position = _ffmpeg_content->video_length ();
+               _audio_position = _ffmpeg_content->audio_length ();
+               return;
        }
 
        avcodec_get_frame_defaults (_frame);
 
        if (_packet.stream_index == _video_stream && _decode_video) {
-
-               int frame_finished;
-               int const r = avcodec_decode_video2 (_video_codec_context, _frame, &frame_finished, &_packet);
-               if (r >= 0 && frame_finished) {
-
-                       if (r != _packet.size) {
-                               _film->log()->log (String::compose (N_("Used only %1 bytes of %2 in packet"), r, _packet.size));
-                       }
-
-                       if (_video_sync) {
-                               out_with_sync ();
-                       } else {
-                               filter_and_emit_video (_frame);
-                       }
-               }
-
+               decode_video_packet ();
        } else if (_ffmpeg_content->audio_stream() && _packet.stream_index == _ffmpeg_content->audio_stream()->id && _decode_audio) {
                decode_audio_packet ();
-       } else if (_ffmpeg_content->subtitle_stream() && _packet.stream_index == _ffmpeg_content->subtitle_stream()->id && _decode_subtitles && _first_video) {
-
-               int got_subtitle;
-               AVSubtitle sub;
-               if (avcodec_decode_subtitle2 (_subtitle_codec_context, &sub, &got_subtitle, &_packet) && got_subtitle) {
-                       /* Sometimes we get an empty AVSubtitle, which is used by some codecs to
-                          indicate that the previous subtitle should stop.
-                       */
-                       if (sub.num_rects > 0) {
-                               shared_ptr<TimedSubtitle> ts;
-                               try {
-                                       emit_subtitle (shared_ptr<TimedSubtitle> (new TimedSubtitle (sub)));
-                               } catch (...) {
-                                       /* some problem with the subtitle; we probably didn't understand it */
-                               }
-                       } else {
-                               emit_subtitle (shared_ptr<TimedSubtitle> ());
-                       }
-                       avsubtitle_free (&sub);
-               }
+       } else if (_ffmpeg_content->subtitle_stream() && _packet.stream_index == _ffmpeg_content->subtitle_stream()->id) {
+               decode_subtitle_packet ();
        }
-       
+
        av_free_packet (&_packet);
-       return false;
 }
 
 /** @param data pointer to array of pointers to buffers.
@@ -389,292 +267,315 @@ FFmpegDecoder::deinterleave_audio (uint8_t** data, int size)
        return audio;
 }
 
-float
-FFmpegDecoder::frames_per_second () const
-{
-       AVStream* s = _format_context->streams[_video_stream];
-
-       if (s->avg_frame_rate.num && s->avg_frame_rate.den) {
-               return av_q2d (s->avg_frame_rate);
-       }
-
-       return av_q2d (s->r_frame_rate);
-}
-
 AVSampleFormat
 FFmpegDecoder::audio_sample_format () const
 {
-       if (_audio_codec_context == 0) {
+       if (!_ffmpeg_content->audio_stream()) {
                return (AVSampleFormat) 0;
        }
        
-       return _audio_codec_context->sample_fmt;
+       return audio_codec_context()->sample_fmt;
 }
 
-libdcp::Size
-FFmpegDecoder::native_size () const
+int
+FFmpegDecoder::bytes_per_audio_sample () const
 {
-       return libdcp::Size (_video_codec_context->width, _video_codec_context->height);
+       return av_get_bytes_per_sample (audio_sample_format ());
 }
 
-PixelFormat
-FFmpegDecoder::pixel_format () const
+void
+FFmpegDecoder::seek (VideoContent::Frame frame, bool accurate)
 {
-       return _video_codec_context->pix_fmt;
-}
+       double const time_base = av_q2d (_format_context->streams[_video_stream]->time_base);
 
-int
-FFmpegDecoder::time_base_numerator () const
-{
-       return _video_codec_context->time_base.num;
-}
+       /* If we are doing an accurate seek, our initial shot will be 5 frames (5 being
+          a number plucked from the air) earlier than we want to end up.  The loop below
+          will hopefully then step through to where we want to be.
+       */
+       int initial = frame;
+       if (accurate) {
+               initial -= 5;
+       }
 
-int
-FFmpegDecoder::time_base_denominator () const
-{
-       return _video_codec_context->time_base.den;
-}
+       if (initial < 0) {
+               initial = 0;
+       }
 
-int
-FFmpegDecoder::sample_aspect_ratio_numerator () const
-{
-       return _video_codec_context->sample_aspect_ratio.num;
-}
+       /* Initial seek time in the stream's timebase */
+       int64_t const initial_vt = ((initial / _ffmpeg_content->video_frame_rate()) - _video_pts_offset) / time_base;
+       /* Wanted final seek time in the stream's timebase */
+       int64_t const final_vt = ((frame / _ffmpeg_content->video_frame_rate()) - _video_pts_offset) / time_base;
 
-int
-FFmpegDecoder::sample_aspect_ratio_denominator () const
-{
-       return _video_codec_context->sample_aspect_ratio.den;
-}
+       av_seek_frame (_format_context, _video_stream, initial_vt, AVSEEK_FLAG_BACKWARD);
 
-string
-FFmpegDecoder::stream_name (AVStream* s) const
-{
-       stringstream n;
-       
-       AVDictionaryEntry const * lang = av_dict_get (s->metadata, N_("language"), 0, 0);
-       if (lang) {
-               n << lang->value;
-       }
-       
-       AVDictionaryEntry const * title = av_dict_get (s->metadata, N_("title"), 0, 0);
-       if (title) {
-               if (!n.str().empty()) {
-                       n << N_(" ");
-               }
-               n << title->value;
+       avcodec_flush_buffers (video_codec_context());
+       if (_subtitle_codec_context) {
+               avcodec_flush_buffers (_subtitle_codec_context);
        }
 
-       if (n.str().empty()) {
-               n << N_("unknown");
+       _just_sought = true;
+
+       if (frame == 0) {
+               /* We're already there; from here on we can only seek non-zero amounts */
+               return;
        }
 
-       return n.str ();
+       if (accurate) {
+               while (1) {
+                       int r = av_read_frame (_format_context, &_packet);
+                       if (r < 0) {
+                               return;
+                       }
+                       
+                       avcodec_get_frame_defaults (_frame);
+                       
+                       if (_packet.stream_index == _video_stream) {
+                               int finished = 0;
+                               int const r = avcodec_decode_video2 (video_codec_context(), _frame, &finished, &_packet);
+                               if (r >= 0 && finished) {
+                                       int64_t const bet = av_frame_get_best_effort_timestamp (_frame);
+                                       if (bet >= final_vt) {
+                                               _video_position = rint (
+                                                       (bet * time_base + _video_pts_offset) * _ffmpeg_content->video_frame_rate()
+                                                       );
+                                               av_free_packet (&_packet);
+                                               break;
+                                       }
+                               }
+                       }
+                       
+                       av_free_packet (&_packet);
+               }
+       }
 }
 
-int
-FFmpegDecoder::bytes_per_audio_sample () const
+void
+FFmpegDecoder::decode_audio_packet ()
 {
-       return av_get_bytes_per_sample (audio_sample_format ());
+       /* Audio packets can contain multiple frames, so we may have to call avcodec_decode_audio4
+          several times.
+       */
+       
+       AVPacket copy_packet = _packet;
+
+       while (copy_packet.size > 0) {
+
+               int frame_finished;
+               int const decode_result = avcodec_decode_audio4 (audio_codec_context(), _frame, &frame_finished, &copy_packet);
+               if (decode_result >= 0) {
+                       if (frame_finished) {
+
+                               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) + _audio_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);
+                                       }
+                               }
+                                       
+                               copy_packet.data += decode_result;
+                               copy_packet.size -= decode_result;
+                       }
+               }
+       }
 }
 
-void
-FFmpegDecoder::filter_and_emit_video (AVFrame* frame)
+bool
+FFmpegDecoder::decode_video_packet ()
 {
+       int frame_finished;
+       if (avcodec_decode_video2 (video_codec_context(), _frame, &frame_finished, &_packet) < 0 || !frame_finished) {
+               return false;
+       }
+
        boost::mutex::scoped_lock lm (_filter_graphs_mutex);
-       
-       shared_ptr<FilterGraph> graph;
 
+       shared_ptr<FilterGraph> graph;
+       
        list<shared_ptr<FilterGraph> >::iterator i = _filter_graphs.begin();
-       while (i != _filter_graphs.end() && !(*i)->can_process (libdcp::Size (frame->width, frame->height), (AVPixelFormat) frame->format)) {
+       while (i != _filter_graphs.end() && !(*i)->can_process (libdcp::Size (_frame->width, _frame->height), (AVPixelFormat) _frame->format)) {
                ++i;
        }
 
        if (i == _filter_graphs.end ()) {
-               graph.reset (new FilterGraph (_film, this, libdcp::Size (frame->width, frame->height), (AVPixelFormat) frame->format));
+               shared_ptr<const Film> film = _film.lock ();
+               assert (film);
+
+               graph.reset (new FilterGraph (_ffmpeg_content, libdcp::Size (_frame->width, _frame->height), (AVPixelFormat) _frame->format));
                _filter_graphs.push_back (graph);
-               _film->log()->log (String::compose (N_("New graph for %1x%2, pixel format %3"), frame->width, frame->height, frame->format));
+
+               film->log()->log (String::compose (N_("New graph for %1x%2, pixel format %3"), _frame->width, _frame->height, _frame->format));
        } else {
                graph = *i;
        }
 
-       list<shared_ptr<Image> > images = graph->process (frame);
+       list<pair<shared_ptr<Image>, int64_t> > images = graph->process (_frame);
 
-       for (list<shared_ptr<Image> >::iterator i = images.begin(); i != images.end(); ++i) {
-               emit_video (*i, frame_time ());
-       }
-}
+       string post_process = Filter::ffmpeg_strings (_ffmpeg_content->filters()).second;
+       
+       for (list<pair<shared_ptr<Image>, int64_t> >::iterator i = images.begin(); i != images.end(); ++i) {
 
-bool
-FFmpegDecoder::seek (double p)
-{
-       return do_seek (p, false);
-}
+               shared_ptr<Image> image = i->first;
+               if (!post_process.empty ()) {
+                       image = image->post_process (post_process, true);
+               }
+               
+               if (i->second != AV_NOPTS_VALUE) {
 
-bool
-FFmpegDecoder::seek_to_last ()
-{
-       /* This AVSEEK_FLAG_BACKWARD in do_seek is a bit of a hack; without it, if we ask for a seek to the same place as last time
-          (used when we change decoder parameters and want to re-fetch the frame) we end up going forwards rather than
-          staying in the same place.
-       */
-       return do_seek (last_source_time(), true);
-}
+                       double const pts = i->second * av_q2d (_format_context->streams[_video_stream]->time_base) + _video_pts_offset;
 
-bool
-FFmpegDecoder::do_seek (double p, bool backwards)
-{
-       int64_t const vt = p / av_q2d (_format_context->streams[_video_stream]->time_base);
+                       if (_just_sought) {
+                               /* We just did a seek, so disable any attempts to correct for where we
+                                  are / should be.
+                               */
+                               _video_position = rint (pts * _ffmpeg_content->video_frame_rate ());
+                               _just_sought = false;
+                       }
 
-       int const r = av_seek_frame (_format_context, _video_stream, vt, backwards ? AVSEEK_FLAG_BACKWARD : 0);
-       
-       avcodec_flush_buffers (_video_codec_context);
-       if (_subtitle_codec_context) {
-               avcodec_flush_buffers (_subtitle_codec_context);
+                       double const next = _video_position / _ffmpeg_content->video_frame_rate();
+                       double const one_frame = 1 / _ffmpeg_content->video_frame_rate ();
+                       double delta = pts - next;
+
+                       while (delta > one_frame) {
+                               /* This PTS is more than one frame forward in time of where we think we should be; emit
+                                  a black frame.
+                               */
+                               boost::shared_ptr<Image> black (
+                                       new Image (
+                                               static_cast<AVPixelFormat> (_frame->format),
+                                               libdcp::Size (video_codec_context()->width, video_codec_context()->height),
+                                               true
+                                               )
+                                       );
+                               
+                               black->make_black ();
+                               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, _video_position);
+                       }
+                               
+               } else {
+                       shared_ptr<const Film> film = _film.lock ();
+                       assert (film);
+                       film->log()->log ("Dropping frame without PTS");
+               }
        }
-       
-       return r < 0;
+
+       return true;
 }
 
+       
 void
-FFmpegDecoder::out_with_sync ()
+FFmpegDecoder::setup_subtitle ()
 {
-       /* Where we are in the output, in seconds */
-       double const out_pts_seconds = video_frame() / frames_per_second();
+       boost::mutex::scoped_lock lm (_mutex);
        
-       /* Where we are in the source, in seconds */
-       double const source_pts_seconds = av_q2d (_format_context->streams[_packet.stream_index]->time_base)
-               * av_frame_get_best_effort_timestamp(_frame);
-       
-       _film->log()->log (
-               String::compose (N_("Source video frame ready; source at %1, output at %2"), source_pts_seconds, out_pts_seconds),
-               Log::VERBOSE
-               );
-       
-       if (!_first_video) {
-               _first_video = source_pts_seconds;
+       if (!_ffmpeg_content->subtitle_stream() || _ffmpeg_content->subtitle_stream()->id >= int (_format_context->nb_streams)) {
+               return;
        }
-       
-       /* Difference between where we are and where we should be */
-       double const delta = source_pts_seconds - _first_video.get() - out_pts_seconds;
-       double const one_frame = 1 / frames_per_second();
-       
-       /* Insert frames if required to get out_pts_seconds up to pts_seconds */
-       if (delta > one_frame) {
-               int const extra = rint (delta / one_frame);
-               for (int i = 0; i < extra; ++i) {
-                       repeat_last_video ();
-                       _film->log()->log (
-                               String::compose (
-                                       N_("Extra video frame inserted at %1s; source frame %2, source PTS %3 (at %4 fps)"),
-                                       out_pts_seconds, video_frame(), source_pts_seconds, frames_per_second()
-                                       )
-                               );
-               }
+
+       _subtitle_codec_context = _format_context->streams[_ffmpeg_content->subtitle_stream()->id]->codec;
+       _subtitle_codec = avcodec_find_decoder (_subtitle_codec_context->codec_id);
+
+       if (_subtitle_codec == 0) {
+               throw DecodeError (_("could not find subtitle decoder"));
        }
        
-       if (delta > -one_frame) {
-               /* Process this frame */
-               filter_and_emit_video (_frame);
-       } else {
-               /* Otherwise we are omitting a frame to keep things right */
-               _film->log()->log (String::compose (N_("Frame removed at %1s"), out_pts_seconds));
+       if (avcodec_open2 (_subtitle_codec_context, _subtitle_codec, 0) < 0) {
+               throw DecodeError (N_("could not open subtitle decoder"));
        }
 }
 
+bool
+FFmpegDecoder::done () const
+{
+       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;
+}
+       
 void
-FFmpegDecoder::film_changed (Film::Property p)
+FFmpegDecoder::decode_subtitle_packet ()
 {
-       switch (p) {
-       case Film::CROP:
-       case Film::FILTERS:
-       {
-               boost::mutex::scoped_lock lm (_filter_graphs_mutex);
-               _filter_graphs.clear ();
+       int got_subtitle;
+       AVSubtitle sub;
+       if (avcodec_decode_subtitle2 (_subtitle_codec_context, &sub, &got_subtitle, &_packet) < 0 || !got_subtitle) {
+               return;
        }
-       OutputChanged ();
-       break;
 
-       default:
-               break;
+       /* Sometimes we get an empty AVSubtitle, which is used by some codecs to
+          indicate that the previous subtitle should stop.
+       */
+       if (sub.num_rects <= 0) {
+               subtitle (shared_ptr<Image> (), dcpomatic::Rect<double> (), 0, 0);
+               return;
+       } else if (sub.num_rects > 1) {
+               throw DecodeError (_("multi-part subtitles not yet supported"));
        }
-}
-
-/** @return Length (in video frames) according to our content's header */
-ContentVideoFrame
-FFmpegDecoder::video_length () const
-{
-       return (double(_format_context->duration) / AV_TIME_BASE) * frames_per_second();
-}
-
-double
-FFmpegDecoder::frame_time () const
-{
-       return av_frame_get_best_effort_timestamp(_frame) * av_q2d (_format_context->streams[_video_stream]->time_base);
-}
-
-void
-FFmpegDecoder::decode_audio_packet ()
-{
-       /* Audio packets can contain multiple frames, so we may have to call avcodec_decode_audio4
-          several times.
+               
+       /* Subtitle PTS in seconds (within the source, not taking into account any of the
+          source that we may have chopped off for the DCP)
        */
+       double const packet_time = static_cast<double> (sub.pts) / AV_TIME_BASE;
        
-       AVPacket copy_packet = _packet;
-
-       while (copy_packet.size > 0) {
+       /* hence start time for this sub */
+       Time const from = (packet_time + (double (sub.start_display_time) / 1e3)) * TIME_HZ;
+       Time const to = (packet_time + (double (sub.end_display_time) / 1e3)) * TIME_HZ;
 
-               int frame_finished;
-               int const decode_result = avcodec_decode_audio4 (_audio_codec_context, _frame, &frame_finished, &copy_packet);
-               if (decode_result >= 0 && 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);
-                       
-                       /* We only decode audio if we've had our first video packet through, and if it
-                          was before this packet.  Until then audio is thrown away.
-                       */
-                       
-                       if ((_first_video && _first_video.get() <= source_pts_seconds) || !_decode_video) {
-                               
-                               if (!_first_audio && _decode_video) {
-                                       _first_audio = source_pts_seconds;
-                                       
-                                       /* This is our first audio frame, and if we've arrived here we must have had our
-                                          first video frame.  Push some silence to make up any gap between our first
-                                          video frame and our first audio.
-                                       */
-                                       
-                                       /* frames of silence that we must push */
-                                       int const s = rint ((_first_audio.get() - _first_video.get()) * _ffmpeg_content->audio_frame_rate ());
-                                       
-                                       _film->log()->log (
-                                               String::compose (
-                                                       N_("First video at %1, first audio at %2, pushing %3 audio frames of silence for %4 channels (%5 bytes per sample)"),
-                                                       _first_video.get(), _first_audio.get(), s, _ffmpeg_content->audio_channels(), bytes_per_audio_sample()
-                                                       )
-                                               );
-                                       
-                                       if (s) {
-                                               shared_ptr<AudioBuffers> audio (new AudioBuffers (_ffmpeg_content->audio_channels(), s));
-                                               audio->make_silent ();
-                                               Audio (audio);
-                                       }
-                               }
-                               
-                               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));
-                       }
-               }
+       AVSubtitleRect const * rect = sub.rects[0];
 
-               if (decode_result >= 0) {
-                       copy_packet.data += decode_result;
-                       copy_packet.size -= decode_result;
-               }
+       if (rect->type != SUBTITLE_BITMAP) {
+               throw DecodeError (_("non-bitmap subtitles not yet supported"));
        }
+       
+       shared_ptr<Image> image (new Image (PIX_FMT_RGBA, libdcp::Size (rect->w, rect->h), true));
+
+       /* Start of the first line in the subtitle */
+       uint8_t* sub_p = rect->pict.data[0];
+       /* sub_p looks up into a RGB palette which is here */
+       uint32_t const * palette = (uint32_t *) rect->pict.data[1];
+       /* Start of the output data */
+       uint32_t* out_p = (uint32_t *) image->data()[0];
+       
+       for (int y = 0; y < rect->h; ++y) {
+               uint8_t* sub_line_p = sub_p;
+               uint32_t* out_line_p = out_p;
+               for (int x = 0; x < rect->w; ++x) {
+                       *out_line_p++ = palette[*sub_line_p++];
+               }
+               sub_p += rect->pict.linesize[0];
+               out_p += image->stride()[0] / sizeof (uint32_t);
+       }
+
+       libdcp::Size const vs = _ffmpeg_content->video_size ();
+
+       subtitle (
+               image,
+               dcpomatic::Rect<double> (
+                       static_cast<double> (rect->x) / vs.width,
+                       static_cast<double> (rect->y) / vs.height,
+                       static_cast<double> (rect->w) / vs.width,
+                       static_cast<double> (rect->h) / vs.height
+                       ),
+               from,
+               to
+               );
+                         
+       
+       avsubtitle_free (&sub);
 }