Seek for video track changes on 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 c686aa9de4c933cbde609efbce9d3c2891c8e694..6a83079c7c6f061102918045144454b267849b1f 100644
--- a/media/filters/ffmpeg_demuxer.cc
+++ b/media/filters/ffmpeg_demuxer.cc
@@ -514,6 +514,12 @@ void FFmpegDemuxerStream::EnqueuePacket(ScopedAVPacket packet) {
     return;
   }
 
+  if (is_audio && last_packet_timestamp_ != kNoTimestamp &&
+      buffer->timestamp() < last_packet_timestamp_) {
+    LOG(ERROR) << "Dropping: " << buffer->timestamp();
+    return;
+  }
+
   // If enabled, and no codec delay is present, mark audio packets with negative
   // timestamps for post-decode discard. If codec delay is present, discard is
   // handled by the decoder using that value.
@@ -1697,8 +1703,22 @@ void FFmpegDemuxer::OnSelectedVideoTrackChanged(
     }
   }
   if (selected_stream) {
-    DVLOG(1) << __func__ << ": enabling stream " << selected_stream;
+    LOG(ERROR) << __func__ << ": enabling stream " << selected_stream;
     selected_stream->set_enabled(true, curr_time);
+    selected_stream->FlushBuffers();
+
+    base::TimeDelta seek_time =
+        start_time_ < base::TimeDelta()
+            ? curr_time + start_time_
+            : curr_time < start_time_ ? start_time_ : curr_time;
+    blocking_task_runner_->PostTask(
+        FROM_HERE,
+        base::Bind(base::IgnoreResult(&av_seek_frame), glue_->format_context(),
+                   selected_stream->av_stream()->index,
+                   ConvertToTimeBase(selected_stream->av_stream()->time_base,
+                                     seek_time),
+                   // Always seek to a timestamp <= to the desired timestamp.
+                   AVSEEK_FLAG_BACKWARD));
   }
 }