Avoid setting alpha mode for H264 webm containers

media/muxers/webm_muxer.cc

 // Copyright 2015 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 "media/muxers/webm_muxer.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/memory/ptr_util.h"
@@ skipping 228 matching lines @@
       reinterpret_cast<mkvmuxer::VideoTrack*>(
           segment_.GetTrackByNumber(video_track_index_));
   DCHECK(video_track);
   video_track->set_codec_id(MkvCodeIcForMediaVideoCodecId(video_codec_));
   DCHECK_EQ(0ull, video_track->crop_right());
   DCHECK_EQ(0ull, video_track->crop_left());
   DCHECK_EQ(0ull, video_track->crop_top());
   DCHECK_EQ(0ull, video_track->crop_bottom());
   DCHECK_EQ(0.0f, video_track->frame_rate());
 
+  // Segment's timestamps should be in milliseconds, DCHECK it. See
+  // http://www.webmproject.org/docs/container/#muxer-guidelines
+  DCHECK_EQ(1000000ull, segment_.GetSegmentInfo()->timecode_scale());
+
+  // Set alpha channel parameters for only VPX, see crbug.com/711825.

[mcasas, 2017/04/14 23:34:51]

nit: "only for VPx (https://crbug.com/711825)."

+  if (video_codec_ == kCodecH264)
+    return;
   video_track->SetAlphaMode(mkvmuxer::VideoTrack::kAlpha);
   // Alpha channel, if present, is stored in a BlockAdditional next to the
   // associated opaque Block, see
   // https://matroska.org/technical/specs/index.html#BlockAdditional.
   // This follows Method 1 for VP8 encoding of A-channel described on
   // http://wiki.webmproject.org/alpha-channel.
   video_track->set_max_block_additional_id(1);
-
-  // Segment's timestamps should be in milliseconds, DCHECK it. See
-  // http://www.webmproject.org/docs/container/#muxer-guidelines
-  DCHECK_EQ(1000000ull, segment_.GetSegmentInfo()->timecode_scale());
 }
 
 void WebmMuxer::AddAudioTrack(const media::AudioParameters& params) {
   DVLOG(1) << __func__ << " " << params.AsHumanReadableString();
   DCHECK(thread_checker_.CalledOnValidThread());
   DCHECK_EQ(0u, audio_track_index_)
       << "WebmMuxer audio can only be initialised once.";
 
   audio_track_index_ =
       segment_.AddAudioTrack(params.sample_rate(), params.channels(), 0);
@@ skipping 96 matching lines @@
     base::TimeTicks timestamp,
     bool is_keyframe)
     : data(std::move(data)),
       alpha_data(std::move(alpha_data)),
       timestamp(timestamp),
       is_keyframe(is_keyframe) {}
 
 WebmMuxer::EncodedVideoFrame::~EncodedVideoFrame() {}
 
 }  // namespace media