Handle Alpha channel in Canvas capture

content/renderer/media/webrtc/webrtc_video_capturer_adapter.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/webrtc/webrtc_video_capturer_adapter.h"
 
 #include "base/bind.h"
 #include "base/memory/aligned_memory.h"
 #include "base/trace_event/trace_event.h"
 #include "content/renderer/media/webrtc/webrtc_video_frame_adapter.h"
@@ skipping 201 matching lines @@
   best_format->height = desired.height;
   best_format->fourcc = cricket::FOURCC_I420;
   best_format->interval = desired.interval;
   return true;
 }
 
 void WebRtcVideoCapturerAdapter::OnFrameCaptured(
     const scoped_refptr<media::VideoFrame>& frame) {
   DCHECK(thread_checker_.CalledOnValidThread());
   TRACE_EVENT0("video", "WebRtcVideoCapturerAdapter::OnFrameCaptured");
-  if (!(frame->IsMappable() && (frame->format() == media::PIXEL_FORMAT_I420 ||
-                                frame->format() == media::PIXEL_FORMAT_YV12))) {
+  if (!(frame->IsMappable() &&
+        (frame->format() == media::PIXEL_FORMAT_I420 ||
+         frame->format() == media::PIXEL_FORMAT_YV12 ||
+         frame->format() == media::PIXEL_FORMAT_YV12A))) {
     // Since connecting sources and sinks do not check the format, we need to
     // just ignore formats that we can not handle.
     NOTREACHED();
     return;
   }
 
+  // Drop alpha channel since we do not support it yet.
+  if (frame->format() == media::PIXEL_FORMAT_YV12A)
+    frame->DropYV12AAlphaChannel();
+
   // Inject the frame via the VideoFrameFactory of base class.
   MediaVideoFrameFactory* media_video_frame_factory =
       reinterpret_cast<MediaVideoFrameFactory*>(frame_factory());
   media_video_frame_factory->SetFrame(frame);
 
   // This signals to libJingle that a new VideoFrame is available.
   SignalFrameCaptured(this, media_video_frame_factory->GetCapturedFrame());
 
   media_video_frame_factory->ReleaseFrame();  // Release the frame ASAP.
 }
 
 }  // namespace content