ExponentialWeightedAverageStatistic.java
/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.media3.exoplayer.upstream.experimental;
import static androidx.media3.exoplayer.upstream.experimental.BandwidthEstimator.ESTIMATE_NOT_AVAILABLE;
import androidx.media3.common.util.UnstableApi;
/** A {@link BandwidthStatistic} that calculates estimates using an exponential weighted average. */
@UnstableApi
public class ExponentialWeightedAverageStatistic implements BandwidthStatistic {
/** The default smoothing factor. */
public static final double DEFAULT_SMOOTHING_FACTOR = 0.9999;
private final double smoothingFactor;
private long bitrateEstimate;
/** Creates an instance with {@link #DEFAULT_SMOOTHING_FACTOR}. */
public ExponentialWeightedAverageStatistic() {
this(DEFAULT_SMOOTHING_FACTOR);
}
/**
* Creates an instance.
*
* @param smoothingFactor The exponential smoothing factor.
*/
public ExponentialWeightedAverageStatistic(double smoothingFactor) {
this.smoothingFactor = smoothingFactor;
bitrateEstimate = ESTIMATE_NOT_AVAILABLE;
}
@Override
public void addSample(long bytes, long durationUs) {
long bitrate = bytes * 8_000_000 / durationUs;
if (bitrateEstimate == ESTIMATE_NOT_AVAILABLE) {
bitrateEstimate = bitrate;
return;
}
// Weight smoothing factor by sqrt(bytes).
double factor = Math.pow(smoothingFactor, Math.sqrt((double) bytes));
bitrateEstimate = (long) (factor * bitrateEstimate + (1f - factor) * bitrate);
}
@Override
public long getBandwidthEstimate() {
return bitrateEstimate;
}
@Override
public void reset() {
bitrateEstimate = ESTIMATE_NOT_AVAILABLE;
}
}