Use ffmpeg packet.pos for restarting reading after reenabling video

media/filters/ffmpeg_demuxer.h

Index: media/filters/ffmpeg_demuxer.h
diff --git a/media/filters/ffmpeg_demuxer.h b/media/filters/ffmpeg_demuxer.h
index bd223ab9ccb8c5fb115e67bd409bd5d80d1bb65c..3d550ca09fb2886c399996097ec73f77969a6a89 100644
--- a/media/filters/ffmpeg_demuxer.h
+++ b/media/filters/ffmpeg_demuxer.h
@@ -271,6 +271,10 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer {
   // FFmpeg callbacks during seeking.
   void OnSeekFrameDone(int result);
 
+  // Called when FFmpeg completes seek initiated in OnSelectedVideoTrackChanged
+  // in order to restart the |stream|.
+  void OnSeekDoneForRestartingStream(FFmpegDemuxerStream* stream, int result);
+
   // FFmpeg callbacks during reading + helper method to initiate reads.
   void ReadFrameIfNeeded();
   void OnReadFrameDone(ScopedAVPacket packet, int result);
@@ -379,6 +383,9 @@ class MEDIA_EXPORT FFmpegDemuxer : public Demuxer {
 
   std::map<MediaTrack::Id, FFmpegDemuxerStream*> track_id_to_demux_stream_map_;
 
+  int64_t last_packet_pos_;
+  FFmpegDemuxerStream* restarting_stream_;
+
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtr<FFmpegDemuxer> weak_this_;
   base::WeakPtrFactory<FFmpegDemuxer> cancel_pending_seek_factory_;