Fix incorrect opus seek preroll and flaky pre-skip removal.

media/filters/ffmpeg_demuxer.cc

Index: media/filters/ffmpeg_demuxer.cc
diff --git a/media/filters/ffmpeg_demuxer.cc b/media/filters/ffmpeg_demuxer.cc
index 80cb7adcbee7a0c13c7630b2d14d4b676db7af61..346a9146511ca449b4867d2cda22c1565095505f 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -270,6 +270,21 @@ void FFmpegDemuxerStream::EnqueuePacket(ScopedAVPacket packet) {
       buffer->set_discard_padding(std::make_pair(
           FramesToTimeDelta(discard_front_samples, samples_per_second),
           FramesToTimeDelta(discard_end_samples, samples_per_second)));
+    } else if (type() == AUDIO && stream_->codec->delay > 0 &&
+               packet->pts <= stream_->start_time &&
+               stream_->codec->codec_id == AV_CODEC_ID_OPUS) {
+      // FFmpeg does not encode the opus pre-skip value within the packet side
+      // data, so when we encounter the first packet in a stream ensure the
+      // codec delay is applied per spec.
+      //
+      // |stream_->codec->delay| has been added to packet->pts automatically by
+      // ffmpeg, so the delta between the start time and the packet pts is the
+      // amount of delay remaining to trim.
+      buffer->set_discard_padding(std::make_pair(
+          FramesToTimeDelta(std::min(static_cast<int64_t>(packet->duration),
+                                     stream_->start_time - packet->pts),
+                            audio_decoder_config().samples_per_second()),
+          base::TimeDelta()));

[wolenetz, 2015/07/29 21:57:27]

Could there be a single packet that is both the start and end of an Opus stream?
If so, then if there is any end sample skipping, this code doesn't work properly
IIUC.

[DaleCurtis, 2015/07/30 01:28:14]

Done.

     }
 
     if (decrypt_config)
@@ -628,9 +643,19 @@ void FFmpegDemuxer::Seek(base::TimeDelta time, const PipelineStatusCB& cb) {
   // Additionally, to workaround limitations in how we expose seekable ranges to
   // Blink (http://crbug.com/137275), we also want to clamp seeks before the
   // start time to the start time.
-  const base::TimeDelta seek_time =
-      start_time_ < base::TimeDelta() ? time + start_time_
-                                      : time < start_time_ ? start_time_ : time;
+  base::TimeDelta seek_time = start_time_ < base::TimeDelta()
+                                  ? time + start_time_
+                                  : time < start_time_ ? start_time_ : time;
+
+  // When seeking in an opus stream we need to ensure we deliver enough data to
+  // satisfy the seek preroll; otherwise the audio at the actual seek time will
+  // not be entirely accurate.
+  FFmpegDemuxerStream* audio_stream = GetFFmpegStream(DemuxerStream::AUDIO);
+  if (audio_stream) {
+    const AudioDecoderConfig& config = audio_stream->audio_decoder_config();
+    if (config.codec() == kCodecOpus)
+      seek_time = std::max(start_time_, seek_time - config.seek_preroll());
+  }
 
   // Choose the seeking stream based on whether it contains the seek time, if no
   // match can be found prefer the preferred stream.
@@ -1204,19 +1229,6 @@ void FFmpegDemuxer::OnReadFrameDone(ScopedAVPacket packet, int result) {
       packet.swap(new_packet);
     }
 
-    // Special case for opus in ogg.  FFmpeg is pre-trimming the codec delay
-    // from the packet timestamp.  Chrome expects to handle this itself inside
-    // the decoder, so shift timestamps by the delay in this case.
-    // TODO(dalecurtis): Try to get fixed upstream.  See http://crbug.com/328207
-    if (strcmp(glue_->format_context()->iformat->name, "ogg") == 0) {
-      const AVCodecContext* codec_context =
-          glue_->format_context()->streams[packet->stream_index]->codec;
-      if (codec_context->codec_id == AV_CODEC_ID_OPUS &&
-          codec_context->delay > 0) {
-        packet->pts += codec_context->delay;
-      }
-    }
-
     FFmpegDemuxerStream* demuxer_stream = streams_[packet->stream_index];
     demuxer_stream->EnqueuePacket(packet.Pass());
   }