H264: Improve FFmpeg decoder performance by using I420BufferPool.

webrtc/common_video/video_frame_buffer.cc

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 63 matching lines @@
       return nullptr;
   }
 }
 
 uint8_t* I420Buffer::MutableData(PlaneType type) {
   RTC_DCHECK(HasOneRef());
   return const_cast<uint8_t*>(
       static_cast<const VideoFrameBuffer*>(this)->data(type));
 }
 
+size_t I420Buffer::DataSize() const {
+  return stride_y_ * height_ + (stride_u_ + stride_v_) * ((height_ + 1) / 2);

[stefan-webrtc, 2016/02/01 14:02:09]

Shouldn't this be the fully allocated size if you are going to use it for
memsetting?

[hbos, 2016/02/02 16:13:03]

This is the size used fir AlignedMalloc and for memset.

Apparently only the data size has to be memset, not the additional bytes due to
alignment:
https://codereview.chromium.org/383893002/diff/1/media/base/video_frame.cc.

This equation is used in two places in this file so I made a helper function.
Also made it return int because the equations was always evaluated as int.

+}
+
 int I420Buffer::stride(PlaneType type) const {
   switch (type) {
     case kYPlane:
       return stride_y_;
     case kUPlane:
       return stride_u_;
     case kVPlane:
       return stride_v_;
     default:
       RTC_NOTREACHED();
@@ skipping 135 matching lines @@
                            buffer->stride(kVPlane) * uv_offset_y + uv_offset_x;
   return new rtc::RefCountedObject<WrappedI420Buffer>(
       cropped_width, cropped_height,
       y_plane, buffer->stride(kYPlane),
       u_plane, buffer->stride(kUPlane),
       v_plane, buffer->stride(kVPlane),
       rtc::KeepRefUntilDone(buffer));
 }
 
 }  // namespace webrtc