modules/video_coding/main/source/frame_dropper.h

/*
 *  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 WEBRTC_MODULES_VIDEO_CODING_FRAME_DROPPER_H_
#define WEBRTC_MODULES_VIDEO_CODING_FRAME_DROPPER_H_

#include "exp_filter.h"
#include "typedefs.h"

namespace webrtc
{

/******************************/
/* VCMFrameDropper class     */
/****************************/
// 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 VCMFrameDropper
{
public:
    VCMFrameDropper(WebRtc_Word32 vcmId = 0);
    // Resets the FrameDropper to its initial state.
    // This means that the frameRateWeight is set to its
    // default value as well.
    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:
    //          - frameSizeBytes    : The size of the latest frame
    //                                returned from the encoder.
    //          - deltaFrame        : True if the encoder returned
    //                                a key frame.
    void Fill(WebRtc_UWord32 frameSizeBytes, bool deltaFrame);

    void Leak(WebRtc_UWord32 inputFrameRate);

    void UpdateNack(WebRtc_UWord32 nackBytes);

    // 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);

    // Return value     : The current average frame rate produced
    //                    if the DropFrame() function is used as
    //                    instruction of when to drop frames.
    float ActualFrameRate(WebRtc_UWord32 inputFrameRate) const;


private:
    void FillBucket(float inKbits, float outKbits);
    void UpdateRatio();
    void CapAccumulator();

    WebRtc_Word32     _vcmId;
    VCMExpFilter       _keyFrameSizeAvgKbits;
    VCMExpFilter       _keyFrameRatio;
    float           _keyFrameSpreadFrames;
    WebRtc_Word32     _keyFrameCount;
    float           _accumulator;
    float           _accumulatorMax;
    float           _targetBitRate;
    bool            _dropNext;
    VCMExpFilter       _dropRatio;
    WebRtc_Word32     _dropCount;
    float           _windowSize;
    float           _incoming_frame_rate;
    bool            _wasBelowMax;
    bool            _enabled;
    bool            _fastMode;
    float           _cap_buffer_size;
    float           _max_time_drops;
}; // end of VCMFrameDropper class

} // namespace webrtc

#endif // WEBRTC_MODULES_VIDEO_CODING_FRAME_DROPPER_H_