Change segment width dynamically in MediaRecorder

media/muxers/webm_muxer.cc

Index: media/muxers/webm_muxer.cc
diff --git a/media/muxers/webm_muxer.cc b/media/muxers/webm_muxer.cc
index 5b98472f875a5f536b9369f7e38fc626f4a6732d..43c0fbf8bc37aab56ce09c5721ce276e455defe9 100644
--- a/media/muxers/webm_muxer.cc
+++ b/media/muxers/webm_muxer.cc
@@ -140,6 +140,17 @@ bool WebmMuxer::OnEncodedVideo(const VideoParameters& params,
   DVLOG(1) << __func__ << " - " << encoded_data->size() << "B";
   DCHECK(thread_checker_.CalledOnValidThread());
 
+  if (!last_frame_size_.IsEmpty() &&
+      last_frame_size_ != params.visible_rect_size) {
+    mkvmuxer::VideoTrack* const video_track =
+        reinterpret_cast<mkvmuxer::VideoTrack*>(
+            segment_.GetTrackByNumber(video_track_index_));
+    DCHECK(video_track);
+    video_track->set_width(params.visible_rect_size.width());
+    video_track->set_height(params.visible_rect_size.height());
+  }
+  last_frame_size_ = params.visible_rect_size;
+
   if (!video_track_index_) {
     // |track_index_|, cannot be zero (!), initialize WebmMuxer in that case.
     // http://www.matroska.org/technical/specs/index.html#Tracks