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* 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) 2020, Unified Streaming.
* 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.
*/
// For a description of the Learn2Adapt-LowLatency (L2A-LL) bitrate adaptation algorithm, see https://github.com/unifiedstreaming/Learn2Adapt-LowLatency/blob/master/Online_learning_for_bitrate_adaptation_in_low_latency_live_streaming_CR.pdf
import MetricsConstants from '../../constants/MetricsConstants.js';
import SwitchRequest from '../SwitchRequest.js';
import FactoryMaker from '../../../core/FactoryMaker.js';
import {HTTPRequest} from '../../vo/metrics/HTTPRequest.js';
import EventBus from '../../../core/EventBus.js';
import Events from '../../../core/events/Events.js';
import Debug from '../../../core/Debug.js';
import Constants from '../../constants/Constants.js';
import Settings from '../../../core/Settings.js';
const L2A_STATE_ONE_BITRATE = 'L2A_STATE_ONE_BITRATE'; // If there is only one bitrate (or initialization failed), always return NO_CHANGE.
const L2A_STATE_STARTUP = 'L2A_STATE_STARTUP'; // Set placeholder buffer such that we download fragments at most recently measured throughput.
const L2A_STATE_STEADY = 'L2A_STATE_STEADY'; // Buffer primed, we switch to steady operation.
const HORIZON = 4; // Optimization horizon (The amount of steps required to achieve convergence)
const VL = Math.pow(HORIZON, 0.99);// Cautiousness parameter, used to control aggressiveness of the bitrate decision process.
const REACT = 2;
function L2ARule(config) {
config = config || {};
const context = this.context;
const dashMetrics = config.dashMetrics;
const eventBus = EventBus(context).getInstance();
const settings = Settings(context).getInstance();
let instance,
l2AStateDict,
l2AParameterDict,
logger;
/**
* Setup function to initialize L2ARule
*/
function setup() {
logger = Debug(context).getInstance().getLogger(instance);
_resetInitialSettings();
eventBus.on(Events.PLAYBACK_SEEKING, _onPlaybackSeeking, instance);
eventBus.on(Events.MEDIA_FRAGMENT_LOADED, _onMediaFragmentLoaded, instance);
eventBus.on(Events.METRIC_ADDED, _onMetricAdded, instance);
}
/**
* Sets the initial state of the algorithm. Calls the initialize function for the paramteters.
* @param {object} rulesContext
* @return {object} initialState
* @private
*/
function _getInitialL2AState(rulesContext) {
const initialState = {};
const mediaInfo = rulesContext.getMediaInfo();
initialState.state = L2A_STATE_STARTUP;
initialState.currentRepresentation = null;
_initializeL2AParameters(mediaInfo);
_clearL2AStateOnSeek(initialState);
return initialState;
}
/**
* Initializes the parameters of the algorithm. This will be done once for each media type.
* @param {object} mediaInfo
* @private
*/
function _initializeL2AParameters(mediaInfo) {
if (!mediaInfo || !mediaInfo.type) {
return;
}
l2AParameterDict[mediaInfo.type] = {};
l2AParameterDict[mediaInfo.type].w = []; //Vector of probabilities associated with bitrate decisions
l2AParameterDict[mediaInfo.type].prev_w = []; //Vector of probabilities associated with bitrate decisions calculated in the previous step
l2AParameterDict[mediaInfo.type].Q = 0; //Initialization of Lagrangian multiplier (This keeps track of the buffer displacement)
l2AParameterDict[mediaInfo.type].segment_request_start_s = 0;
l2AParameterDict[mediaInfo.type].segment_download_finish_s = 0;
l2AParameterDict[mediaInfo.type].B_target = 1.5; //Target buffer level
}
/**
* Clears the state object
* @param {object} l2AState
* @private
*/
function _clearL2AStateOnSeek(l2AState) {
l2AState.placeholderBuffer = 0;
l2AState.mostAdvancedSegmentStart = NaN;
l2AState.lastSegmentWasReplacement = false;
l2AState.lastSegmentStart = NaN;
l2AState.lastSegmentDurationS = NaN;
l2AState.lastSegmentRequestTimeMs = NaN;
l2AState.lastSegmentFinishTimeMs = NaN;
l2AState.lastSegmentUrl = '';
}
/**
* Returns the state object for a fiven media type. If the state object is not yet defined _getInitialL2AState is called
* @param {object} rulesContext
* @return {object} l2AState
* @private
*/
function _getL2AState(rulesContext) {
const mediaType = rulesContext.getMediaType();
let l2AState = l2AStateDict[mediaType];
if (!l2AState) {
l2AState = _getInitialL2AState(rulesContext);
l2AStateDict[mediaType] = l2AState;
}
return l2AState;
}
/**
* Event handler for the seeking event.
* @private
*/
function _onPlaybackSeeking() {
for (const mediaType in l2AStateDict) {
if (l2AStateDict.hasOwnProperty(mediaType)) {
const l2aState = l2AStateDict[mediaType];
if (l2aState.state !== L2A_STATE_ONE_BITRATE) {
l2aState.state = L2A_STATE_STARTUP;
_clearL2AStateOnSeek(l2aState);
}
}
}
}
/**
* Event handler for the mediaFragmentLoaded event
* @param {object} e
* @private
*/
function _onMediaFragmentLoaded(e) {
if (e && e.chunk && e.chunk.representation && e.chunk.representation.mediaInfo) {
const l2AState = l2AStateDict[e.chunk.representation.mediaInfo.type];
const l2AParameters = l2AParameterDict[e.chunk.representation.mediaInfo.type];
if (l2AState && l2AState.state !== L2A_STATE_ONE_BITRATE) {
const start = e.chunk.start;
if (isNaN(l2AState.mostAdvancedSegmentStart) || start > l2AState.mostAdvancedSegmentStart) {
l2AState.mostAdvancedSegmentStart = start;
l2AState.lastSegmentWasReplacement = false;
} else {
l2AState.lastSegmentWasReplacement = true;
}
l2AState.lastSegmentStart = start;
l2AState.lastSegmentDurationS = e.chunk.duration;
l2AState.currentRepresentation = e.chunk.representation;
_checkNewSegment(l2AState, l2AParameters);
}
}
}
/**
* Event handler for the metricAdded event
* @param {object} e
* @private
*/
function _onMetricAdded(e) {
if (e && e.metric === MetricsConstants.HTTP_REQUEST && e.value && e.value.type === HTTPRequest.MEDIA_SEGMENT_TYPE && e.value.trace && e.value.trace.length) {
const l2AState = l2AStateDict[e.mediaType];
const l2AParameters = l2AParameterDict[e.mediaType];
if (l2AState && l2AState.state !== L2A_STATE_ONE_BITRATE) {
l2AState.lastSegmentRequestTimeMs = e.value.trequest.getTime();
l2AState.lastSegmentFinishTimeMs = e.value._tfinish.getTime();
_checkNewSegment(l2AState, l2AParameters);
}
}
}
/**
* When a new metric has been added or a media fragment has been loaded the state is adjusted accordingly
* @param {object} L2AState
* @param {object} l2AParameters
* @private
*/
function _checkNewSegment(L2AState, l2AParameters) {
if (!isNaN(L2AState.lastSegmentStart) && !isNaN(L2AState.lastSegmentRequestTimeMs)) {
l2AParameters.segment_request_start_s = 0.001 * L2AState.lastSegmentRequestTimeMs;
l2AParameters.segment_download_finish_s = 0.001 * L2AState.lastSegmentFinishTimeMs;
L2AState.lastSegmentStart = NaN;
L2AState.lastSegmentRequestTimeMs = NaN;
}
}
/**
* Dot multiplication of two arrays
* @param {array} arr1
* @param {array} arr2
* @return {number} sumdot
* @private
*/
function _dotmultiplication(arr1, arr2) {
if (arr1.length !== arr2.length) {
return -1;
}
let sumdot = 0;
for (let i = 0; i < arr1.length; i++) {
sumdot = sumdot + arr1[i] * arr2[i];
}
return sumdot;
}
/**
* Project an n-dim vector y to the simplex Dn
* Dn = { x : x n-dim, 1 >= x >= 0, sum(x) = 1}
* Algorithm is explained at http://arxiv.org/abs/1101.6081
* @param {array} arr
* @return {array}
*/
function euclideanProjection(arr) {
const m = arr.length;
let bget = false;
let arr2 = [];
for (let ii = 0; ii < m; ++ii) {
arr2[ii] = arr[ii];
}
let s = arr.sort(function (a, b) {
return b - a;
});
let tmpsum = 0;
let tmax = 0;
let x = [];
for (let ii = 0; ii < m - 1; ++ii) {
tmpsum = tmpsum + s[ii];
tmax = (tmpsum - 1) / (ii + 1);
if (tmax >= s[ii + 1]) {
bget = true;
break;
}
}
if (!bget) {
tmax = (tmpsum + s[m - 1] - 1) / m;
}
for (let ii = 0; ii < m; ++ii) {
x[ii] = Math.max(arr2[ii] - tmax, 0);
}
return x;
}
/**
*
* @param rulesContext
* @param switchRequest
* @param l2AState
* @private
*/
function _handleStartupState(rulesContext, switchRequest, l2AState) {
const mediaInfo = rulesContext.getMediaInfo();
const mediaType = rulesContext.getMediaType();
const throughputController = rulesContext.getThroughputController();
const safeThroughput = throughputController.getSafeAverageThroughput(mediaType);
if (isNaN(safeThroughput)) {
// still starting up - not enough information
return switchRequest;
}
const abrController = rulesContext.getAbrController();
const representation = abrController.getOptimalRepresentationForBitrate(mediaInfo, safeThroughput, true);//During strat-up phase abr.controller is responsible for bitrate decisions.
const bufferLevel = dashMetrics.getCurrentBufferLevel(mediaType, true);
const l2AParameter = l2AParameterDict[mediaType];
const possibleRepresentations = abrController.getPossibleVoRepresentationsFilteredBySettings(mediaInfo, true);
switchRequest.representation = representation;
switchRequest.reason.throughput = safeThroughput;
l2AState.currentRepresentation = representation;
if (!isNaN(l2AState.lastSegmentDurationS) && bufferLevel >= l2AParameter.B_target) {
l2AState.state = L2A_STATE_STEADY;
l2AParameter.Q = VL;// Initialization of Q langrangian multiplier
// Update of probability vector w, to be used in main adaptation logic of L2A below (steady state)
for (let i = 0; i < possibleRepresentations.length; ++i) {
const rep = possibleRepresentations[i];
if (rep.id === l2AState.currentRepresentation.id) {
l2AParameter.prev_w[i] = 1;
} else {
l2AParameter.prev_w[i] = 0;
}
}
}
}
function _handleSteadyState(rulesContext, switchRequest, l2AState) {
let diff1 = []; //Used to calculate the difference between consecutive decisions (w-w_prev)
const throughputController = rulesContext.getThroughputController();
const mediaType = rulesContext.getMediaType();
let lastThroughput = throughputController.getAverageThroughput(mediaType, Constants.THROUGHPUT_CALCULATION_MODES.ARITHMETIC_MEAN, 1);
let currentHttpRequest = dashMetrics.getCurrentHttpRequest(mediaType);
let selectedRepresentation = null;
const l2AParameter = l2AParameterDict[mediaType];
//To avoid division with 0 (avoid infinity) in case of an absolute network outage
if (lastThroughput < 1) {
lastThroughput = 1;
}
// Note that for SegmentBase addressing the request url does not change.
// As this is not relevant for low latency streaming at this point the check below is sufficient
if (currentHttpRequest.url === l2AState.lastSegmentUrl ||
currentHttpRequest.type === HTTPRequest.INIT_SEGMENT_TYPE) {
// No change to inputs or init segment so use previously calculated quality
selectedRepresentation = l2AState.currentRepresentation;
} else { // Recalculate Q
let V = l2AState.lastSegmentDurationS;
let sign = 1;
//Main adaptation logic of L2A-LL
const abrController = rulesContext.getAbrController();
const mediaInfo = rulesContext.getMediaInfo();
const possibleRepresentations = abrController.getPossibleVoRepresentationsFilteredBySettings(mediaInfo, true);
const videoModel = rulesContext.getVideoModel();
let currentPlaybackRate = videoModel.getPlaybackRate();
const alpha = Math.max(Math.pow(HORIZON, 1), VL * Math.sqrt(HORIZON));// Step size, used for gradient descent exploration granularity
for (let i = 0; i < possibleRepresentations.length; ++i) {
const rep = possibleRepresentations[i];
// In this case buffer would deplete, leading to a stall, which increases latency and thus the particular probability of selection of bitrate[i] should be decreased.
if (currentPlaybackRate * rep.bitrateInKbit > lastThroughput) {
sign = -1;
}
// The objective of L2A is to minimize the overall latency=request-response time + buffer length after download+ potential stalling (if buffer less than chunk downlad time)
l2AParameter.w[i] = l2AParameter.prev_w[i] + sign * (V / (2 * alpha)) * ((l2AParameter.Q + VL) * (currentPlaybackRate * rep.bitrateInKbit / lastThroughput));//Lagrangian descent
}
// Apply euclidean projection on w to ensure w expresses a probability distribution
l2AParameter.w = euclideanProjection(l2AParameter.w);
for (let i = 0; i < possibleRepresentations.length; ++i) {
diff1[i] = l2AParameter.w[i] - l2AParameter.prev_w[i];
l2AParameter.prev_w[i] = l2AParameter.w[i];
}
// Lagrangian multiplier Q calculation:
const bitrates = possibleRepresentations.map((rep) => {
return rep.bandwidth;
})
l2AParameter.Q = Math.max(0, l2AParameter.Q - V + V * currentPlaybackRate * ((_dotmultiplication(bitrates, l2AParameter.prev_w) + _dotmultiplication(bitrates, diff1)) / lastThroughput));
// Quality is calculated as argmin of the absolute difference between available bitrates (bitrates[i]) and bitrate estimation (dotmultiplication(w,bitrates)).
let temp = [];
for (let i = 0; i < bitrates.length; ++i) {
temp[i] = Math.abs(bitrates[i] - _dotmultiplication(l2AParameter.w, bitrates));
}
// Quality is calculated based on the probability distribution w (the output of L2A)
const absoluteIndex = temp.indexOf(Math.min(...temp));
selectedRepresentation = abrController.getRepresentationByAbsoluteIndex(absoluteIndex, mediaInfo, true);
// We employ a cautious -stepwise- ascent
if (selectedRepresentation.absoluteIndex > l2AState.currentRepresentation.absoluteIndex) {
if (bitrates[l2AState.currentRepresentation.absoluteIndex + 1] <= lastThroughput) {
selectedRepresentation = abrController.getRepresentationByAbsoluteIndex(l2AState.currentRepresentation.absoluteIndex + 1, mediaInfo, true);
}
}
// Provision against bitrate over-estimation, by re-calibrating the Lagrangian multiplier Q, to be taken into account for the next chunk
if (selectedRepresentation.bitrateInKbit >= lastThroughput) {
l2AParameter.Q = REACT * Math.max(VL, l2AParameter.Q);
}
l2AState.lastSegmentUrl = currentHttpRequest.url;
}
switchRequest.representation = selectedRepresentation;
l2AState.currentRepresentation = switchRequest.representation;
}
function _handleErrorState(rulesContext, switchRequest, l2AState) {
const abrController = rulesContext.getAbrController();
const mediaInfo = rulesContext.getMediaInfo();
const mediaType = rulesContext.getMediaType();
const throughputController = rulesContext.getThroughputController();
const safeThroughput = throughputController.getSafeAverageThroughput(mediaType);
switchRequest.representation = abrController.getOptimalRepresentationForBitrate(mediaInfo, safeThroughput, true);//During strat-up phase abr.controller is responsible for bitrate decisions.
switchRequest.reason.throughput = safeThroughput;
l2AState.state = L2A_STATE_STARTUP;
_clearL2AStateOnSeek(l2AState);
}
/**
* Returns a switch request object indicating which quality is to be played
* @param {object} rulesContext
* @return {object}
*/
function getSwitchRequest(rulesContext) {
try {
const switchRequest = SwitchRequest(context).create();
switchRequest.rule = this.getClassName();
const mediaType = rulesContext.getMediaType();
const scheduleController = rulesContext.getScheduleController();
switchRequest.reason = switchRequest.reason || {};
// L2A decides bitrate only for video. Audio to be included in decision process in a later stage
if ((mediaType === Constants.AUDIO)) {
return switchRequest;
}
scheduleController.setTimeToLoadDelay(0);
const l2AState = _getL2AState(rulesContext);
const l2AParameter = l2AParameterDict[mediaType];
if (!l2AParameter) {
return switchRequest;
}
switchRequest.reason.state = l2AState.state;
switch (l2AState.state) {
case L2A_STATE_ONE_BITRATE:
break;
case L2A_STATE_STARTUP:
_handleStartupState(rulesContext, switchRequest, l2AState);
break;
case L2A_STATE_STEADY:
_handleSteadyState(rulesContext, switchRequest, l2AState);
break;
default:
_handleErrorState(rulesContext, switchRequest, l2AState)
}
switchRequest.priority = settings.get().streaming.abr.rules.l2ARule.priority;
return switchRequest;
} catch (e) {
logger.error(e);
return SwitchRequest(context).create();
}
}
/**
* Reset objects to their initial state
* @private
*/
function _resetInitialSettings() {
l2AStateDict = {};
l2AParameterDict = {};
}
/**
* Reset the rule
*/
function reset() {
_resetInitialSettings();
eventBus.off(Events.PLAYBACK_SEEKING, _onPlaybackSeeking, instance);
eventBus.off(Events.MEDIA_FRAGMENT_LOADED, _onMediaFragmentLoaded, instance);
eventBus.off(Events.METRIC_ADDED, _onMetricAdded, instance);
}
instance = {
getSwitchRequest,
reset
};
setup();
return instance;
}
L2ARule.__dashjs_factory_name = 'L2ARule';
export default FactoryMaker.getClassFactory(L2ARule);
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