Set FFmpeg AVStream discard on FFmpeg task runner thread

media/filters/ffmpeg_demuxer.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Implements the Demuxer interface using FFmpeg's libavformat.  At this time
 // will support demuxing any audio/video format thrown at it.  The streams
 // output mime types audio/x-ffmpeg and video/x-ffmpeg and include an integer
 // key FFmpegCodecID which contains the CodecID enumeration value.  The CodecIDs
 // can be used to create and initialize the corresponding FFmpeg decoder.
 //
@@ skipping 235 matching lines @@
   // |track_id| either contains the selected video track id or is null,
   // indicating that all video tracks are deselected/disabled.
   void OnSelectedVideoTrackChanged(base::Optional<MediaTrack::Id> track_id,
                                    base::TimeDelta curr_time) override;
 
   // The lowest demuxed timestamp.  If negative, DemuxerStreams must use this to
   // adjust packet timestamps such that external clients see a zero-based
   // timeline.
   base::TimeDelta start_time() const { return start_time_; }
 
+  // Task runner used to execute blocking FFmpeg operations.
+  scoped_refptr<base::SequencedTaskRunner> ffmpeg_task_runner() {
+    return blocking_task_runner_;
+  }
+
  private:
   // To allow tests access to privates.
   friend class FFmpegDemuxerTest;
 
   // FFmpeg callbacks during initialization.
   void OnOpenContextDone(const PipelineStatusCB& status_cb, bool result);
   void OnFindStreamInfoDone(const PipelineStatusCB& status_cb, int result);
 
   void LogMetadata(AVFormatContext* avctx, base::TimeDelta max_duration);
 
@@ skipping 112 matching lines @@
   base::WeakPtr<FFmpegDemuxer> weak_this_;
   base::WeakPtrFactory<FFmpegDemuxer> cancel_pending_seek_factory_;
   base::WeakPtrFactory<FFmpegDemuxer> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(FFmpegDemuxer);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_FFMPEG_DEMUXER_H_