Set AVDISCARD_ALL flag for disabled streams in FFmpegDemuxer

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 d329492be4808fca7491f6b9fbe49c523f48f805..19a6f250b5d3655872ef051e95f75494f2408f12 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -732,6 +732,7 @@ void FFmpegDemuxerStream::set_enabled(bool enabled, base::TimeDelta timestamp) {
     return;
 
   is_enabled_ = enabled;
+  av_stream()->discard = enabled ? AVDISCARD_DEFAULT : AVDISCARD_ALL;
   if (is_enabled_) {
     waiting_for_keyframe_ = true;
   }
@@ -1287,9 +1288,11 @@ void FFmpegDemuxer::OnFindStreamInfoDone(const PipelineStatusCB& status_cb,
     } else if (codec_type == AVMEDIA_TYPE_SUBTITLE) {
       detected_text_track_count++;
       if (codec_id != AV_CODEC_ID_WEBVTT || !text_enabled_) {
+        stream->discard = AVDISCARD_ALL;
         continue;
       }
     } else {
+      stream->discard = AVDISCARD_ALL;
       continue;
     }