Handle Alpha channel in Canvas capture

content/renderer/media/video_track_recorder.cc

Index: content/renderer/media/video_track_recorder.cc
diff --git a/content/renderer/media/video_track_recorder.cc b/content/renderer/media/video_track_recorder.cc
index e95999a5d40861076f40550cde1dfda049950ecc..9c1bbd628ae049e92f539abb886f6fcd81fddc3c 100644
--- a/content/renderer/media/video_track_recorder.cc
+++ b/content/renderer/media/video_track_recorder.cc
@@ -14,6 +14,7 @@
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "media/base/video_frame.h"
+#include "media/base/video_util.h"
 #include "ui/gfx/geometry/size.h"
 
 extern "C" {
@@ -186,12 +187,23 @@ void VideoTrackRecorder::VpxEncoder::StartFrameEncode(
 }
 
 void VideoTrackRecorder::VpxEncoder::EncodeOnEncodingThread(
-    const scoped_refptr<VideoFrame>& frame,
+    const scoped_refptr<VideoFrame>& video_frame,
     base::TimeTicks capture_timestamp) {
   TRACE_EVENT0("video",
                "VideoTrackRecorder::VpxEncoder::EncodeOnEncodingThread");
   DCHECK(encoding_thread_->task_runner()->BelongsToCurrentThread());
 
+  if (!(video_frame->format() == media::PIXEL_FORMAT_I420 ||
+        video_frame->format() == media::PIXEL_FORMAT_YV12 ||
+        video_frame->format() == media::PIXEL_FORMAT_YV12A)) {
+    NOTREACHED();
+    return;
+  }
+  scoped_refptr<media::VideoFrame> frame = video_frame;
+  // Drop alpha channel since we do not support it yet.
+  if (frame->format() == media::PIXEL_FORMAT_YV12A)
+    frame = media::WrapAsI420VideoFrame(video_frame);
+
   const gfx::Size frame_size = frame->visible_rect().size();
   if (!IsInitialized() ||
       gfx::Size(codec_config_.g_w, codec_config_.g_h) != frame_size) {