Allow media track switching.

media/video/gpu_memory_buffer_video_frame_pool.h

 // 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.
 
 #ifndef MEDIA_VIDEO_GPU_MEMORY_BUFFER_VIDEO_FRAME_POOL_H_
 #define MEDIA_VIDEO_GPU_MEMORY_BUFFER_VIDEO_FRAME_POOL_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/task_runner.h"
 #include "media/base/video_frame.h"
 
 namespace base {
 class SingleThreadTaskRunner;
 }
 
 namespace media {
 class GpuVideoAcceleratorFactories;
 
 // Interface to a pool of GpuMemoryBuffers/textures/images that can be used to
 // transform software VideoFrames to VideoFrames backed by native textures.
 // The resources used by the VideoFrame created by the pool will be
 // automatically put back into the pool once the frame is destroyed.
 // The pool recycles resources to a void unnecessarily allocating and
 // destroying textures, images and GpuMemoryBuffer that could result
 // in a round trip to the browser/GPU process.
+// NOTE: Destroying the pool will not immediately invalidate outstanding video
+// frames. GPU memory buffers will be kept alive by video frames indirectly
+// referencing them. Video frames themselves are ref-counted and will be
+// released when they are no longer needed, potentially after the pool is
+// destroyed.
 class MEDIA_EXPORT GpuMemoryBufferVideoFramePool {
  public:
   GpuMemoryBufferVideoFramePool();
   GpuMemoryBufferVideoFramePool(
       const scoped_refptr<base::SingleThreadTaskRunner>& media_task_runner,
       const scoped_refptr<base::TaskRunner>& worker_task_runner,
       GpuVideoAcceleratorFactories* gpu_factories);
   virtual ~GpuMemoryBufferVideoFramePool();
 
   // Callback used by MaybeCreateHardwareFrame to deliver a new VideoFrame
@@ skipping 14 matching lines @@
  private:
   class PoolImpl;
   scoped_refptr<PoolImpl> pool_impl_;
 
   DISALLOW_COPY_AND_ASSIGN(GpuMemoryBufferVideoFramePool);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_VIDEO_GPU_MEMORY_BUFFER_VIDEO_FRAME_POOL_H_