frame_dropper.h - mozsearch

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/*

 *  Copyright (c) 2011 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 MODULES_VIDEO_CODING_UTILITY_FRAME_DROPPER_H_

#define MODULES_VIDEO_CODING_UTILITY_FRAME_DROPPER_H_

#include <stddef.h>

#include <stdint.h>

#include "rtc_base/numerics/exp_filter.h"

namespace webrtc {

// The Frame Dropper implements a variant of the leaky bucket algorithm

// for keeping track of when to drop frames to avoid bit rate

// over use when the encoder can't keep its bit rate.

class FrameDropper {

 public:

  FrameDropper();

  ~FrameDropper();

  // Resets the FrameDropper to its initial state.

  void Reset();

  void Enable(bool enable);

  // Answers the question if it's time to drop a frame if we want to reach a

  // given frame rate. Must be called for every frame.

//

  // Return value     : True if we should drop the current frame.

  bool DropFrame();

  // Updates the FrameDropper with the size of the latest encoded frame.

  // The FrameDropper calculates a new drop ratio (can be seen as the

  // probability to drop a frame) and updates its internal statistics.

//

  // Input:

  //          - framesize_bytes    : The size of the latest frame returned

  //                                 from the encoder.

  //          - delta_frame        : True if the encoder returned a delta frame.

  void Fill(size_t framesize_bytes, bool delta_frame);

  void Leak(uint32_t input_framerate);

  // Sets the target bit rate and the frame rate produced by the camera.

//

  // Input:

  //          - bitrate       : The target bit rate.

  void SetRates(float bitrate, float incoming_frame_rate);

 private:

  void UpdateRatio();

  void CapAccumulator();

  rtc::ExpFilter key_frame_ratio_;

  rtc::ExpFilter delta_frame_size_avg_kbits_;

  // Key frames and large delta frames are not immediately accumulated in the

  // bucket since they can immediately overflow the bucket leading to large

  // drops on the following packets that may be much smaller. Instead these

  // large frames are accumulated over several frames when the bucket leaks.

  // `large_frame_accumulation_spread_` represents the number of frames over

  // which a large frame is accumulated.

  float large_frame_accumulation_spread_;

  // `large_frame_accumulation_count_` represents the number of frames left

  // to finish accumulating a large frame.

  int large_frame_accumulation_count_;

  // `large_frame_accumulation_chunk_size_` represents the size of a single

  // chunk for large frame accumulation.

  float large_frame_accumulation_chunk_size_;

  float accumulator_;

  float accumulator_max_;

  float target_bitrate_;

  bool drop_next_;

  rtc::ExpFilter drop_ratio_;

  int drop_count_;

  float incoming_frame_rate_;

  bool was_below_max_;

  bool enabled_;

  const float max_drop_duration_secs_;

};

}  // namespace webrtc

#endif  // MODULES_VIDEO_CODING_UTILITY_FRAME_DROPPER_H_