H264: Improve FFmpeg decoder performance by using I420BufferPool.

webrtc/modules/video_coding/codecs/h264/h264_decoder_impl.h

 /*
  *  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.
  *
  */
 
 #ifndef WEBRTC_MODULES_VIDEO_CODING_CODECS_H264_H264_DECODER_IMPL_H_
 #define WEBRTC_MODULES_VIDEO_CODING_CODECS_H264_H264_DECODER_IMPL_H_
 
 #include "webrtc/modules/video_coding/codecs/h264/include/h264.h"
 
 extern "C" {
 #include "third_party/ffmpeg/libavcodec/avcodec.h"
 }  // extern "C"
 
 #include "webrtc/base/scoped_ptr.h"
+#include "webrtc/common_video/include/i420_buffer_pool.h"
 
 namespace webrtc {
 
 struct AVCodecContextDeleter {
   void operator()(AVCodecContext* ptr) const { avcodec_free_context(&ptr); }
 };
 struct AVFrameDeleter {
   void operator()(AVFrame* ptr) const { av_frame_free(&ptr); }
 };
 
@@ skipping 13 matching lines @@
       DecodedImageCallback* callback) override;
 
   // |missing_frames|, |fragmentation| and |render_time_ms| are ignored.
   int32_t Decode(const EncodedImage& input_image,
                  bool /*missing_frames*/,
                  const RTPFragmentationHeader* /*fragmentation*/,
                  const CodecSpecificInfo* codec_specific_info = nullptr,
                  int64_t render_time_ms = -1) override;
 
  private:
+  // Called by FFmpeg when it needs a frame buffer to store decoded frames in.
+  // The |VideoFrame| returned by FFmpeg at |Decode| originate from here. Their
+  // buffers are reference counted and freed by FFmpeg using |AVFreeBuffer2|.
+  static int AVGetBuffer2(
+      AVCodecContext* context, AVFrame* av_frame, int flags);
+  // Called by FFmpeg when it is done with a video frame, see |AVGetBuffer2|.
+  static void AVFreeBuffer2(void* opaque, uint8_t* data);
+
   bool IsInitialized() const;
 
+  I420BufferPool pool_;
   rtc::scoped_ptr<AVCodecContext, AVCodecContextDeleter> av_context_;
   rtc::scoped_ptr<AVFrame, AVFrameDeleter> av_frame_;
 
   DecodedImageCallback* decoded_image_callback_;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_VIDEO_CODING_CODECS_H264_H264_DECODER_IMPL_H_