Extract bitrate allocation of spatial/temporal layers out of codec impl.

webrtc/modules/video_coding/utility/default_video_bitrate_allocator.h

+/*
+ *  Copyright (c) 2016 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_UTILITY_DEFAULT_VIDEO_BITRATE_ALLOCATOR_H_
+#define WEBRTC_MODULES_VIDEO_CODING_UTILITY_DEFAULT_VIDEO_BITRATE_ALLOCATOR_H_
+
+#include "webrtc/common_video/include/video_bitrate_allocator.h"
+
+namespace webrtc {
+
+class DefaultVideoBitrateAllocator : public VideoBitrateAllocator {
+ public:
+  explicit DefaultVideoBitrateAllocator(const VideoCodec& codec);
+  ~DefaultVideoBitrateAllocator() override;
+
+  BitrateAllocation GetAllocation(uint32_t total_bitrate,
+                                  uint32_t framerate) override;
+  uint32_t GetPreferedBitrate(int frame_rate) override;
+
+ private:
+  const VideoCodec codec_;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_VIDEO_CODING_UTILITY_DEFAULT_VIDEO_BITRATE_ALLOCATOR_H_