@l5i/dashjs
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A reference client implementation for the playback of MPEG DASH via Javascript and compliant browsers.
256 lines (214 loc) • 11.3 kB
JavaScript
/**
* The copyright in this software is being made available under the BSD License,
* included below. This software may be subject to other third party and contributor
* rights, including patent rights, and no such rights are granted under this license.
*
* Copyright (c) 2017, Dash Industry Forum.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without modification,
* are permitted provided that the following conditions are met:
* * Redistributions of source code must retain the above copyright notice, this
* list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation and/or
* other materials provided with the distribution.
* * Neither the name of Dash Industry Forum nor the names of its
* contributors may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS AS IS AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
* INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
* WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/
import Constants from '../constants/Constants';
import FactoryMaker from '../../core/FactoryMaker';
// throughput generally stored in kbit/s
// latency generally stored in ms
function ThroughputHistory(config) {
config = config || {};
// sliding window constants
const MAX_MEASUREMENTS_TO_KEEP = 20;
const AVERAGE_THROUGHPUT_SAMPLE_AMOUNT_LIVE = 3;
const AVERAGE_THROUGHPUT_SAMPLE_AMOUNT_VOD = 4;
const AVERAGE_LATENCY_SAMPLE_AMOUNT = 4;
const THROUGHPUT_DECREASE_SCALE = 1.3;
const THROUGHPUT_INCREASE_SCALE = 1.3;
// EWMA constants
const EWMA_THROUGHPUT_SLOW_HALF_LIFE_SECONDS = 8;
const EWMA_THROUGHPUT_FAST_HALF_LIFE_SECONDS = 3;
const EWMA_LATENCY_SLOW_HALF_LIFE_COUNT = 2;
const EWMA_LATENCY_FAST_HALF_LIFE_COUNT = 1;
const mediaPlayerModel = config.mediaPlayerModel;
let throughputDict,
latencyDict,
ewmaThroughputDict,
ewmaLatencyDict,
ewmaHalfLife;
function setup() {
ewmaHalfLife = {
throughputHalfLife: { fast: EWMA_THROUGHPUT_FAST_HALF_LIFE_SECONDS, slow: EWMA_THROUGHPUT_SLOW_HALF_LIFE_SECONDS },
latencyHalfLife: { fast: EWMA_LATENCY_FAST_HALF_LIFE_COUNT, slow: EWMA_LATENCY_SLOW_HALF_LIFE_COUNT }
};
reset();
}
function isCachedResponse(mediaType, latencyMs, downloadTimeMs) {
if (mediaType === Constants.VIDEO) {
return downloadTimeMs < mediaPlayerModel.getCacheLoadThresholdForType(Constants.VIDEO);
} else if (mediaType === Constants.AUDIO) {
return downloadTimeMs < mediaPlayerModel.getCacheLoadThresholdForType(Constants.AUDIO);
}
}
function push(mediaType, httpRequest, useDeadTimeLatency) {
if (!httpRequest.trace || !httpRequest.trace.length) {
return;
}
const latencyTimeInMilliseconds = (httpRequest.tresponse.getTime() - httpRequest.trequest.getTime()) || 1;
const downloadTimeInMilliseconds = (httpRequest._tfinish.getTime() - httpRequest.tresponse.getTime()) || 1; //Make sure never 0 we divide by this value. Avoid infinity!
const downloadTime = httpRequest.trace.reduce((a, b) => a + b.d, 0);
const downloadBytes = httpRequest.trace.reduce((a, b) => a + b.b[0], 0);
let throughputMeasureTime = useDeadTimeLatency ? downloadTimeInMilliseconds : latencyTimeInMilliseconds + downloadTimeInMilliseconds;
throughputMeasureTime = mediaPlayerModel.getLowLatencyEnabled() ? downloadTime : throughputMeasureTime;
const throughput = Math.round((8 * downloadBytes) / throughputMeasureTime); // bits/ms = kbits/s
checkSettingsForMediaType(mediaType);
if (isCachedResponse(mediaType, latencyTimeInMilliseconds, downloadTimeInMilliseconds)) {
if (throughputDict[mediaType].length > 0 && !throughputDict[mediaType].hasCachedEntries) {
// already have some entries which are not cached entries
// prevent cached fragment loads from skewing the average values
return;
} else { // have no entries || have cached entries
// no uncached entries yet, rely on cached entries because ABR rules need something to go by
throughputDict[mediaType].hasCachedEntries = true;
}
} else if (throughputDict[mediaType] && throughputDict[mediaType].hasCachedEntries) {
// if we are here then we have some entries already, but they are cached, and now we have a new uncached entry
clearSettingsForMediaType(mediaType);
}
throughputDict[mediaType].push(throughput);
if (throughputDict[mediaType].length > MAX_MEASUREMENTS_TO_KEEP) {
throughputDict[mediaType].shift();
}
latencyDict[mediaType].push(latencyTimeInMilliseconds);
if (latencyDict[mediaType].length > MAX_MEASUREMENTS_TO_KEEP) {
latencyDict[mediaType].shift();
}
updateEwmaEstimate(ewmaThroughputDict[mediaType], throughput, 0.001 * downloadTimeInMilliseconds, ewmaHalfLife.throughputHalfLife);
updateEwmaEstimate(ewmaLatencyDict[mediaType], latencyTimeInMilliseconds, 1, ewmaHalfLife.latencyHalfLife);
}
function updateEwmaEstimate(ewmaObj, value, weight, halfLife) {
// Note about startup:
// Estimates start at 0, so early values are underestimated.
// This effect is countered in getAverageEwma() by dividing the estimates by:
// 1 - Math.pow(0.5, ewmaObj.totalWeight / halfLife)
const fastAlpha = Math.pow(0.5, weight / halfLife.fast);
ewmaObj.fastEstimate = (1 - fastAlpha) * value + fastAlpha * ewmaObj.fastEstimate;
const slowAlpha = Math.pow(0.5, weight / halfLife.slow);
ewmaObj.slowEstimate = (1 - slowAlpha) * value + slowAlpha * ewmaObj.slowEstimate;
ewmaObj.totalWeight += weight;
}
function getSampleSize(isThroughput, mediaType, isLive) {
let arr,
sampleSize;
if (isThroughput) {
arr = throughputDict[mediaType];
sampleSize = isLive ? AVERAGE_THROUGHPUT_SAMPLE_AMOUNT_LIVE : AVERAGE_THROUGHPUT_SAMPLE_AMOUNT_VOD;
} else {
arr = latencyDict[mediaType];
sampleSize = AVERAGE_LATENCY_SAMPLE_AMOUNT;
}
if (!arr) {
sampleSize = 0;
} else if (sampleSize >= arr.length) {
sampleSize = arr.length;
} else if (isThroughput) {
// if throughput samples vary a lot, average over a wider sample
for (let i = 1; i < sampleSize; ++i) {
const ratio = arr[i] / arr[i - 1];
if (ratio >= THROUGHPUT_INCREASE_SCALE || ratio <= 1 / THROUGHPUT_DECREASE_SCALE) {
sampleSize += 1;
if (sampleSize === arr.length) { // cannot increase sampleSize beyond arr.length
break;
}
}
}
}
return sampleSize;
}
function getAverage(isThroughput, mediaType, isDynamic) {
// only two moving average methods defined at the moment
return mediaPlayerModel.getMovingAverageMethod() !== Constants.MOVING_AVERAGE_SLIDING_WINDOW ?
getAverageEwma(isThroughput, mediaType) : getAverageSlidingWindow(isThroughput, mediaType, isDynamic);
}
function getAverageSlidingWindow(isThroughput, mediaType, isDynamic) {
const sampleSize = getSampleSize(isThroughput, mediaType, isDynamic);
const dict = isThroughput ? throughputDict : latencyDict;
let arr = dict[mediaType];
if (sampleSize === 0 || !arr || arr.length === 0) {
return NaN;
}
arr = arr.slice(-sampleSize); // still works if sampleSize too large
// arr.length >= 1
return arr.reduce((total, elem) => total + elem) / arr.length;
}
function getAverageEwma(isThroughput, mediaType) {
const halfLife = isThroughput ? ewmaHalfLife.throughputHalfLife : ewmaHalfLife.latencyHalfLife;
const ewmaObj = isThroughput ? ewmaThroughputDict[mediaType] : ewmaLatencyDict[mediaType];
if (!ewmaObj || ewmaObj.totalWeight <= 0) {
return NaN;
}
// to correct for startup, divide by zero factor = 1 - Math.pow(0.5, ewmaObj.totalWeight / halfLife)
const fastEstimate = ewmaObj.fastEstimate / (1 - Math.pow(0.5, ewmaObj.totalWeight / halfLife.fast));
const slowEstimate = ewmaObj.slowEstimate / (1 - Math.pow(0.5, ewmaObj.totalWeight / halfLife.slow));
return isThroughput ? Math.min(fastEstimate, slowEstimate) : Math.max(fastEstimate, slowEstimate);
}
function getAverageThroughput(mediaType, isDynamic) {
return getAverage(true, mediaType, isDynamic);
}
function getSafeAverageThroughput(mediaType, isDynamic) {
let average = getAverageThroughput(mediaType, isDynamic);
if (!isNaN(average)) {
average *= mediaPlayerModel.getBandwidthSafetyFactor();
}
return average;
}
function getAverageLatency(mediaType) {
return getAverage(false, mediaType);
}
function checkSettingsForMediaType(mediaType) {
throughputDict[mediaType] = throughputDict[mediaType] || [];
latencyDict[mediaType] = latencyDict[mediaType] || [];
ewmaThroughputDict[mediaType] = ewmaThroughputDict[mediaType] || {fastEstimate: 0, slowEstimate: 0, totalWeight: 0};
ewmaLatencyDict[mediaType] = ewmaLatencyDict[mediaType] || {fastEstimate: 0, slowEstimate: 0, totalWeight: 0};
}
function clearSettingsForMediaType(mediaType) {
delete throughputDict[mediaType];
delete latencyDict[mediaType];
delete ewmaThroughputDict[mediaType];
delete ewmaLatencyDict[mediaType];
checkSettingsForMediaType(mediaType);
}
function reset() {
throughputDict = {};
latencyDict = {};
ewmaThroughputDict = {};
ewmaLatencyDict = {};
}
const instance = {
push: push,
getAverageThroughput: getAverageThroughput,
getSafeAverageThroughput: getSafeAverageThroughput,
getAverageLatency: getAverageLatency,
reset: reset
};
setup();
return instance;
}
ThroughputHistory.__dashjs_factory_name = 'ThroughputHistory';
export default FactoryMaker.getClassFactory(ThroughputHistory);