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/*
* Copyright (c) 2020 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.audio;
import android.media.AudioTrack;
import android.os.Build;
import org.webrtc.Logging;
// Lowers the buffer size if no underruns are detected for 100 ms. Once an
// underrun is detected, the buffer size is increased by 10 ms and it will not
// be lowered further. The buffer size will never be increased more than
// 5 times, to avoid the possibility of the buffer size increasing without
// bounds.
class LowLatencyAudioBufferManager {
private static final String TAG = "LowLatencyAudioBufferManager";
// The underrun count that was valid during the previous call to maybeAdjustBufferSize(). Used to
// detect increases in the value.
private int prevUnderrunCount;
// The number of ticks to wait without an underrun before decreasing the buffer size.
private int ticksUntilNextDecrease;
// Indicate if we should continue to decrease the buffer size.
private boolean keepLoweringBufferSize;
// How often the buffer size was increased.
private int bufferIncreaseCounter;
public LowLatencyAudioBufferManager() {
this.prevUnderrunCount = 0;
this.ticksUntilNextDecrease = 10;
this.keepLoweringBufferSize = true;
this.bufferIncreaseCounter = 0;
}
public void maybeAdjustBufferSize(AudioTrack audioTrack) {
if (Build.VERSION.SDK_INT >= 26) {
final int underrunCount = audioTrack.getUnderrunCount();
if (underrunCount > prevUnderrunCount) {
// Don't increase buffer more than 5 times. Continuing to increase the buffer size
// could be harmful on low-power devices that regularly experience underruns under
// normal conditions.
if (bufferIncreaseCounter < 5) {
// Underrun detected, increase buffer size by 10ms.
final int currentBufferSize = audioTrack.getBufferSizeInFrames();
final int newBufferSize = currentBufferSize + audioTrack.getPlaybackRate() / 100;
Logging.d(TAG,
"Underrun detected! Increasing AudioTrack buffer size from " + currentBufferSize
+ " to " + newBufferSize);
audioTrack.setBufferSizeInFrames(newBufferSize);
bufferIncreaseCounter++;
}
// Stop trying to lower the buffer size.
keepLoweringBufferSize = false;
prevUnderrunCount = underrunCount;
ticksUntilNextDecrease = 10;
} else if (keepLoweringBufferSize) {
ticksUntilNextDecrease--;
if (ticksUntilNextDecrease <= 0) {
// No underrun seen for 100 ms, try to lower the buffer size by 10ms.
final int bufferSize10ms = audioTrack.getPlaybackRate() / 100;
// Never go below a buffer size of 10ms.
final int currentBufferSize = audioTrack.getBufferSizeInFrames();
final int newBufferSize = Math.max(bufferSize10ms, currentBufferSize - bufferSize10ms);
if (newBufferSize != currentBufferSize) {
Logging.d(TAG,
"Lowering AudioTrack buffer size from " + currentBufferSize + " to "
+ newBufferSize);
audioTrack.setBufferSizeInFrames(newBufferSize);
}
ticksUntilNextDecrease = 10;
}
}
}
}
}