Upstream Gentoo Linux patch for using system ffmpeg

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 28b376c0436ccbab07e102bdc145f19ca65a58d8..136fe32a7b9ab469020a8e9c0a606af25c3cb0ef 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -1247,6 +1247,7 @@ void FFmpegDemuxer::OnFindStreamInfoDone(const PipelineStatusCB& status_cb,
   // If no estimate is found, the stream entry will be kInfiniteDuration.
   std::vector<base::TimeDelta> start_time_estimates(format_context->nb_streams,
                                                     kInfiniteDuration);
+#if !defined(USE_SYSTEM_FFMPEG)
   const AVFormatInternal* internal = format_context->internal;
   if (internal && internal->packet_buffer &&
       format_context->start_time != static_cast<int64_t>(AV_NOPTS_VALUE)) {
@@ -1270,6 +1271,7 @@ void FFmpegDemuxer::OnFindStreamInfoDone(const PipelineStatusCB& status_cb,
       packet_buffer = packet_buffer->next;
     }
   }
+#endif  // !defined(USE_SYSTEM_FFMPEG)
 
   std::unique_ptr<MediaTracks> media_tracks(new MediaTracks());