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/*
* Copyright 2017 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.
*/
package org.webrtc;
/**
* BitrateAdjuster that tracks the bandwidth produced by an encoder and dynamically adjusts the
* bitrate. Used for hardware codecs that pay attention to framerate but still deviate from the
* target bitrate by unacceptable margins.
*/
class DynamicBitrateAdjuster extends BaseBitrateAdjuster {
// Change the bitrate at most once every three seconds.
private static final double BITRATE_ADJUSTMENT_SEC = 3.0;
// Maximum bitrate adjustment scale - no more than 4 times.
private static final double BITRATE_ADJUSTMENT_MAX_SCALE = 4;
// Amount of adjustment steps to reach maximum scale.
private static final int BITRATE_ADJUSTMENT_STEPS = 20;
private static final double BITS_PER_BYTE = 8.0;
// How far the codec has deviated above (or below) the target bitrate (tracked in bytes).
private double deviationBytes;
private double timeSinceLastAdjustmentMs;
private int bitrateAdjustmentScaleExp;
@Override
public void setTargets(int targetBitrateBps, double targetFramerateFps) {
if (this.targetBitrateBps > 0 && targetBitrateBps < this.targetBitrateBps) {
// Rescale the accumulator level if the accumulator max decreases
deviationBytes = deviationBytes * targetBitrateBps / this.targetBitrateBps;
}
super.setTargets(targetBitrateBps, targetFramerateFps);
}
@Override
public void reportEncodedFrame(int size) {
if (targetFramerateFps == 0) {
return;
}
// Accumulate the difference between actual and expected frame sizes.
double expectedBytesPerFrame = (targetBitrateBps / BITS_PER_BYTE) / targetFramerateFps;
deviationBytes += (size - expectedBytesPerFrame);
timeSinceLastAdjustmentMs += 1000.0 / targetFramerateFps;
// Adjust the bitrate when the encoder accumulates one second's worth of data in excess or
// shortfall of the target.
double deviationThresholdBytes = targetBitrateBps / BITS_PER_BYTE;
// Cap the deviation, i.e., don't let it grow beyond some level to avoid using too old data for
// bitrate adjustment. This also prevents taking more than 3 "steps" in a given 3-second cycle.
double deviationCap = BITRATE_ADJUSTMENT_SEC * deviationThresholdBytes;
deviationBytes = Math.min(deviationBytes, deviationCap);
deviationBytes = Math.max(deviationBytes, -deviationCap);
// Do bitrate adjustment every 3 seconds if actual encoder bitrate deviates too much
// from the target value.
if (timeSinceLastAdjustmentMs <= 1000 * BITRATE_ADJUSTMENT_SEC) {
return;
}
if (deviationBytes > deviationThresholdBytes) {
// Encoder generates too high bitrate - need to reduce the scale.
int bitrateAdjustmentInc = (int) (deviationBytes / deviationThresholdBytes + 0.5);
bitrateAdjustmentScaleExp -= bitrateAdjustmentInc;
// Don't let the adjustment scale drop below -BITRATE_ADJUSTMENT_STEPS.
// This sets a minimum exponent of -1 (bitrateAdjustmentScaleExp / BITRATE_ADJUSTMENT_STEPS).
bitrateAdjustmentScaleExp = Math.max(bitrateAdjustmentScaleExp, -BITRATE_ADJUSTMENT_STEPS);
deviationBytes = deviationThresholdBytes;
} else if (deviationBytes < -deviationThresholdBytes) {
// Encoder generates too low bitrate - need to increase the scale.
int bitrateAdjustmentInc = (int) (-deviationBytes / deviationThresholdBytes + 0.5);
bitrateAdjustmentScaleExp += bitrateAdjustmentInc;
// Don't let the adjustment scale exceed BITRATE_ADJUSTMENT_STEPS.
// This sets a maximum exponent of 1 (bitrateAdjustmentScaleExp / BITRATE_ADJUSTMENT_STEPS).
bitrateAdjustmentScaleExp = Math.min(bitrateAdjustmentScaleExp, BITRATE_ADJUSTMENT_STEPS);
deviationBytes = -deviationThresholdBytes;
}
timeSinceLastAdjustmentMs = 0;
}
private double getBitrateAdjustmentScale() {
return Math.pow(BITRATE_ADJUSTMENT_MAX_SCALE,
(double) bitrateAdjustmentScaleExp / BITRATE_ADJUSTMENT_STEPS);
}
@Override
public int getAdjustedBitrateBps() {
return (int) (targetBitrateBps * getBitrateAdjustmentScale());
}
}