[Cast] VideoFrameFactory interface to vend frames with encoder affinity.

media/cast/sender/video_frame_factory.h

+// Copyright 2014 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_CAST_SENDER_VIDEO_FRAME_FACTORY_H_
+#define MEDIA_CAST_SENDER_VIDEO_FRAME_FACTORY_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
+
+namespace media {
+
+class VideoFrame;
+
+namespace cast {
+
+// Interface for an object capable of vending video frames. There is no
+// requirement for a |VideoFrameFactory| to be concurrent but it must not be
+// pinned to a specific thread. Indeed, |VideoFrameFactory| implementations are
+// created by cast on the main cast thread then used by unknown client threads
+// via the |VideoFrameInput| interface.
+//
+// Clients are responsible for serialzing access to a |VideoFrameFactory|.
+// Generally speaking, it is expected that a client will be using these objects
+// from a rendering thread or callback (which may execute on different threads
+// but never concurrently with itself). Forcing every implementation to take a
+// lock, even with no contention, is an unnecessary cost, especially on mobile
+// platforms.
+class VideoFrameFactory {
+ public:
+  virtual ~VideoFrameFactory() {}
+
+  // Creates a |VideoFrame| suitable for input via |InsertRawVideoFrame|. Frames
+  // obtained in this manner may provide benefits such memory reuse and affinity
+  // with the encoder. The format is guaranteed to be I420 or NV12.
+  virtual scoped_refptr<VideoFrame> CreateFrame(base::TimeDelta timestamp) = 0;
+};
+
+}  // namespace cast
+}  // namespace media
+
+#endif  // MEDIA_CAST_SENDER_VIDEO_FRAME_FACTORY_H_