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A reference client implementation for the playback of MPEG DASH via Javascript and compliant browsers.
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<h1 class="page-title">Source: streaming/controllers/CatchupController.js</h1>
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<pre
class="sunlight-highlight-javascript linenums">/**
* 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) 2013, 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 FactoryMaker from '../../core/FactoryMaker';
import Debug from '../../core/Debug';
import EventBus from '../../core/EventBus';
import Constants from '../constants/Constants';
import MediaPlayerEvents from '../MediaPlayerEvents';
import Events from '../../core/events/Events';
import MetricsConstants from '../constants/MetricsConstants';
import Utils from '../../core/Utils';
function CatchupController() {
const context = this.context;
const eventBus = EventBus(context).getInstance();
let instance,
isCatchupSeekInProgress,
isSafari,
videoModel,
settings,
streamController,
playbackController,
mediaPlayerModel,
playbackStalled,
logger;
function initialize() {
_registerEvents();
}
function setConfig(config) {
if (!config) {
return;
}
if (config.settings) {
settings = config.settings;
}
if (config.videoModel) {
videoModel = config.videoModel;
}
if (config.streamController) {
streamController = config.streamController;
}
if (config.playbackController) {
playbackController = config.playbackController;
}
if (config.mediaPlayerModel) {
mediaPlayerModel = config.mediaPlayerModel;
}
}
function _registerEvents() {
eventBus.on(MediaPlayerEvents.BUFFER_LEVEL_UPDATED, _onBufferLevelUpdated, instance);
eventBus.on(MediaPlayerEvents.BUFFER_LEVEL_STATE_CHANGED, _onBufferLevelStateChanged, instance);
eventBus.on(MediaPlayerEvents.PLAYBACK_PROGRESS, _onPlaybackProgression, instance);
eventBus.on(MediaPlayerEvents.PLAYBACK_TIME_UPDATED, _onPlaybackProgression, instance);
eventBus.on(MediaPlayerEvents.PLAYBACK_SEEKED, _onPlaybackSeeked, instance);
eventBus.on(Events.SETTING_UPDATED_CATCHUP_ENABLED, _onCatchupSettingUpdated, instance);
}
function _unregisterEvents() {
eventBus.off(MediaPlayerEvents.BUFFER_LEVEL_UPDATED, _onBufferLevelUpdated, instance);
eventBus.off(MediaPlayerEvents.BUFFER_LEVEL_STATE_CHANGED, _onBufferLevelStateChanged, instance);
eventBus.off(MediaPlayerEvents.PLAYBACK_PROGRESS, _onPlaybackProgression, instance);
eventBus.off(MediaPlayerEvents.PLAYBACK_TIME_UPDATED, _onPlaybackProgression, instance);
eventBus.off(MediaPlayerEvents.PLAYBACK_SEEKED, _onPlaybackProgression, instance);
eventBus.off(Events.SETTING_UPDATED_CATCHUP_ENABLED, _onCatchupSettingUpdated, instance);
}
function setup() {
logger = Debug(context).getInstance().getLogger(instance);
_resetInitialSettings();
}
function reset() {
_unregisterEvents();
_resetInitialSettings();
videoModel.setPlaybackRate(1.0, true);
}
function _resetInitialSettings() {
isCatchupSeekInProgress = false;
const ua = Utils.parseUserAgent();
isSafari = ua && ua.browser && ua.browser.name && ua.browser.name.toLowerCase() === 'safari';
}
function _onPlaybackSeeked() {
isCatchupSeekInProgress = false;
}
/**
* When the buffer level updated we check if we can remove the stalled state
* @param {object} e
* @private
*/
function _onBufferLevelUpdated(e) {
// do not stop when getting an event from Stream that is not active
if (e.streamId !== streamController.getActiveStreamInfo().id || !playbackStalled) {
return;
}
// we remove the stalled state once we reach a certain buffer level
const liveDelay = playbackController.getLiveDelay();
const bufferLevel = playbackController.getBufferLevel();
if (bufferLevel > liveDelay / 2) {
playbackStalled = false;
}
}
/**
* When the buffer state changed to BUFFER_EMPTY we update the stalled state
* @param {object} e
* @private
*/
function _onBufferLevelStateChanged(e) {
// do not stop when getting an event from Stream that is not active
if (e.streamId !== streamController.getActiveStreamInfo().id) {
return;
}
playbackStalled = e.state === MetricsConstants.BUFFER_EMPTY;
}
/**
* If the catchup mode is disabled in the settings we reset playback rate to 1.0
* @private
*/
function _onCatchupSettingUpdated() {
if (!mediaPlayerModel.getCatchupModeEnabled()) {
videoModel.setPlaybackRate(1.0);
}
}
/**
* While playback is progressing we check if we need to start or stop the catchup mechanism to reach the target latency
* @private
*/
function _onPlaybackProgression() {
if (playbackController.getIsDynamic() && mediaPlayerModel.getCatchupModeEnabled() && mediaPlayerModel.getCatchupPlaybackRate() > 0 && !playbackController.isPaused() && !playbackController.isSeeking() && _shouldStartCatchUp()) {
_startPlaybackCatchUp();
}
}
/**
* Apply catchup mode. We either seek back to the target live edge or increase the playback rate.
*/
function _startPlaybackCatchUp() {
// we are seeking dont do anything for now
if (isCatchupSeekInProgress) {
return;
}
if (videoModel) {
let newRate;
const currentPlaybackRate = videoModel.getPlaybackRate();
const liveCatchupPlaybackRate = mediaPlayerModel.getCatchupPlaybackRate();
const bufferLevel = playbackController.getBufferLevel();
const deltaLatency = _getLatencyDrift();
// we reached the maxDrift. Do a seek
const maxDrift = mediaPlayerModel.getCatchupMaxDrift();
if (!isNaN(maxDrift) && maxDrift > 0 &&
deltaLatency > maxDrift) {
logger.info('[CatchupController]: Low Latency catchup mechanism. Latency too high, doing a seek to live point');
isCatchupSeekInProgress = true;
playbackController.seekToCurrentLive(true, false);
}
// try to reach the target latency by adjusting the playback rate
else {
const currentLiveLatency = playbackController.getCurrentLiveLatency();
const targetLiveDelay = playbackController.getLiveDelay();
if (_getCatchupMode() === Constants.LIVE_CATCHUP_MODE_LOLP) {
// Custom playback control: Based on buffer level
const playbackBufferMin = settings.get().streaming.liveCatchup.playbackBufferMin;
newRate = _calculateNewPlaybackRateLolP(liveCatchupPlaybackRate, currentLiveLatency, targetLiveDelay, playbackBufferMin, bufferLevel, currentPlaybackRate);
} else {
// Default playback control: Based on target and current latency
newRate = _calculateNewPlaybackRateDefault(liveCatchupPlaybackRate, currentLiveLatency, targetLiveDelay, bufferLevel, currentPlaybackRate);
}
// We adjust the min change linear, depending on the maximum catchup rate. Default is 0.02 for rate 0.5.
// For Safari we stick to a fixed value because of https://bugs.webkit.org/show_bug.cgi?id=208142
const minPlaybackRateChange = isSafari ? 0.25 : 0.02 / (0.5 / liveCatchupPlaybackRate);
// Obtain newRate and apply to video model. Don't change playbackrate for small variations (don't overload element with playbackrate changes)
if (newRate && Math.abs(currentPlaybackRate - newRate) >= minPlaybackRateChange) { // non-null
logger.debug(`[CatchupController]: Setting playback rate to ${newRate}`);
videoModel.setPlaybackRate(newRate);
}
}
}
}
/**
* Calculates the drift between the current latency and the target latency
* @return {number}
* @private
*/
function _getLatencyDrift() {
const currentLiveLatency = playbackController.getCurrentLiveLatency();
const targetLiveDelay = playbackController.getLiveDelay();
return currentLiveLatency - targetLiveDelay;
}
/**
* Checks whether the catchup mechanism should be enabled. We use different subfunctions here depending on the catchup mode.
* @return {boolean}
*/
function _shouldStartCatchUp() {
try {
if (!playbackController.getTime() > 0 || isCatchupSeekInProgress) {
return false;
}
const catchupMode = _getCatchupMode();
if (catchupMode === Constants.LIVE_CATCHUP_MODE_LOLP) {
const currentBuffer = playbackController.getBufferLevel();
const playbackBufferMin = settings.get().streaming.liveCatchup.playbackBufferMin;
return _lolpNeedToCatchUpCustom(currentBuffer, playbackBufferMin);
} else {
return _defaultNeedToCatchUp();
}
} catch (e) {
return false;
}
}
/**
* Returns the mode for live playback catchup.
* @return {String}
* @private
*/
function _getCatchupMode() {
const playbackBufferMin = settings.get().streaming.liveCatchup.playbackBufferMin;
return settings.get().streaming.liveCatchup.mode === Constants.LIVE_CATCHUP_MODE_LOLP && playbackBufferMin !== null && !isNaN(playbackBufferMin) ? Constants.LIVE_CATCHUP_MODE_LOLP : Constants.LIVE_CATCHUP_MODE_DEFAULT;
}
/**
* Default algorithm to determine if catchup mode should be enabled
* @return {boolean}
* @private
*/
function _defaultNeedToCatchUp() {
try {
const latencyDrift = Math.abs(_getLatencyDrift());
return latencyDrift > 0;
} catch (e) {
return false;
}
}
/**
* LoL+ logic to determine if catchup mode should be enabled
* @param {number} currentBuffer
* @param {number} playbackBufferMin
* @return {boolean}
* @private
*/
function _lolpNeedToCatchUpCustom(currentBuffer, playbackBufferMin) {
try {
const latencyDrift = Math.abs(_getLatencyDrift());
return latencyDrift > 0 || currentBuffer < playbackBufferMin;
} catch (e) {
return false;
}
}
/**
* Default algorithm to calculate the new playback rate
* @param {number} liveCatchUpPlaybackRate
* @param {number} currentLiveLatency
* @param {number} liveDelay
* @param {number} bufferLevel
* @param {number} currentPlaybackRate
* @return {number}
* @private
*/
function _calculateNewPlaybackRateDefault(liveCatchUpPlaybackRate, currentLiveLatency, liveDelay, bufferLevel) {
// if we recently ran into an empty buffer we wait for the buffer to recover before applying a new rate
if (playbackStalled) {
return 1.0;
}
const cpr = liveCatchUpPlaybackRate;
const deltaLatency = currentLiveLatency - liveDelay;
const d = deltaLatency * 5;
// Playback rate must be between (1 - cpr) - (1 + cpr)
// ex: if cpr is 0.5, it can have values between 0.5 - 1.5
const s = (cpr * 2) / (1 + Math.pow(Math.E, -d));
let newRate = (1 - cpr) + s;
// take into account situations in which there are buffer stalls,
// in which increasing playbackRate to reach target latency will
// just cause more and more stall situations
if (playbackController.getPlaybackStalled()) {
if (bufferLevel <= liveDelay / 2 && deltaLatency > 0) {
newRate = 1.0;
}
}
return newRate;
}
/**
* Lol+ algorithm to calculate the new playback rate
* @param {number} liveCatchUpPlaybackRate
* @param {number} currentLiveLatency
* @param {number} liveDelay
* @param {number} playbackBufferMin
* @param {number} bufferLevel
* @param {number} currentPlaybackRate
* @return {number}
* @private
*/
function _calculateNewPlaybackRateLolP(liveCatchUpPlaybackRate, currentLiveLatency, liveDelay, playbackBufferMin, bufferLevel) {
const cpr = liveCatchUpPlaybackRate;
let newRate;
// Hybrid: Buffer-based
if (bufferLevel < playbackBufferMin) {
// Buffer in danger, slow down
const deltaBuffer = bufferLevel - playbackBufferMin; // -ve value
const d = deltaBuffer * 5;
// Playback rate must be between (1 - cpr) - (1 + cpr)
// ex: if cpr is 0.5, it can have values between 0.5 - 1.5
const s = (cpr * 2) / (1 + Math.pow(Math.E, -d));
newRate = (1 - cpr) + s;
logger.debug('[LoL+ playback control_buffer-based] bufferLevel: ' + bufferLevel + ', newRate: ' + newRate);
} else {
// Hybrid: Latency-based
// Buffer is safe, vary playback rate based on latency
// Check if latency is within range of target latency
const minDifference = 0.02;
if (Math.abs(currentLiveLatency - liveDelay) <= (minDifference * liveDelay)) {
newRate = 1;
} else {
const deltaLatency = currentLiveLatency - liveDelay;
const d = deltaLatency * 5;
// Playback rate must be between (1 - cpr) - (1 + cpr)
// ex: if cpr is 0.5, it can have values between 0.5 - 1.5
const s = (cpr * 2) / (1 + Math.pow(Math.E, -d));
newRate = (1 - cpr) + s;
}
logger.debug('[LoL+ playback control_latency-based] latency: ' + currentLiveLatency + ', newRate: ' + newRate);
}
return newRate
}
instance = {
reset,
setConfig,
initialize
};
setup();
return instance;
}
CatchupController.__dashjs_factory_name = 'CatchupController';
export default FactoryMaker.getSingletonFactory(CatchupController);
</pre>
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