H264: Improve FFmpeg decoder performance by using I420BufferPool.

webrtc/common_video/i420_buffer_pool.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 35 matching lines @@
   }
 
   friend class rtc::RefCountedObject<PooledI420Buffer>;
   rtc::scoped_refptr<webrtc::I420Buffer> buffer_;
 };
 
 }  // namespace
 
 namespace webrtc {
 
-I420BufferPool::I420BufferPool() {
+I420BufferPool::I420BufferPool(bool zero_initialize)
+    : zero_initialize_(zero_initialize) {
   Release();
 }
 
 void I420BufferPool::Release() {
   thread_checker_.DetachFromThread();
   buffers_.clear();
 }
 
 rtc::scoped_refptr<VideoFrameBuffer> I420BufferPool::CreateBuffer(int width,
                                                                   int height) {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
   // Release buffers with wrong resolution.
   for (auto it = buffers_.begin(); it != buffers_.end();) {
     if ((*it)->width() != width || (*it)->height() != height)
       it = buffers_.erase(it);
     else
       ++it;
   }
   // Look for a free buffer.
   for (const rtc::scoped_refptr<I420Buffer>& buffer : buffers_) {
     // If the buffer is in use, the ref count will be 2, one from the list we
     // are looping over and one from a PooledI420Buffer returned from
     // CreateBuffer that has not been released yet. If the ref count is 1
     // (HasOneRef), then the list we are looping over holds the only reference
     // and it's safe to reuse.
     if (buffer->HasOneRef())
       return new rtc::RefCountedObject<PooledI420Buffer>(buffer);
   }
   // Allocate new buffer.
-  buffers_.push_back(new rtc::RefCountedObject<I420Buffer>(width, height));
+  rtc::scoped_refptr<I420Buffer> buffer = new rtc::RefCountedObject<I420Buffer>(
+      width, height);
+  if (zero_initialize_)
+    memset(buffer->MutableData(kYPlane), 0, buffer->DataSize());

[stefan-webrtc, 2016/02/01 14:02:08]

Is it safe to assume continuous memory here?

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

Yes because it is a pool specifically for I420Buffers which are continuous.
Didn't DCHECK because I420Buffer does not contain |aligned_size| like VideoFrame
does and didn't think it was worth adding.

+  buffers_.push_back(buffer);
   return new rtc::RefCountedObject<PooledI420Buffer>(buffers_.back());
 }
 
 }  // namespace webrtc