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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/models/LowLatencyThroughputModel.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 Debug from '../../core/Debug';
import FactoryMaker from '../../core/FactoryMaker';
function LowLatencyThroughputModel() {
const LLTM_MAX_MEASUREMENTS = 10;
// factor (<1) is used to reduce the real needed download time when at very bleeding live edge
const LLTM_SEMI_OPTIMISTIC_ESTIMATE_FACTOR = 0.8;
const LLTM_OPTIMISTIC_ESTIMATE_FACTOR = 0.6;
const LLTM_SLOW_SEGMENT_DOWNLOAD_TOLERANCE = 1.05;
const LLTM_MAX_DELAY_MS = 250;
const context = this.context;
let instance;
let logger;
let measurements = {};
function setup() {
logger = Debug(context).getInstance().getLogger(instance);
}
/**
* Linear regression with least squares method to get a trend function for buffer lavel at chunk receive timestamps
* @param {*} chunkMeasurements
* @returns linear trend function
*/
function createBufferLevelTrendFunction(chunkMeasurements) {
const result = {};
let sumX = 0
let sumY = 0
let sumXY = 0
let sumXSq = 0
const N = chunkMeasurements.length
for (var i = 0; i < N; ++i) {
sumX += chunkMeasurements[i].chunkDownloadTimeRelativeMS;
sumY += chunkMeasurements[i].bufferLevel;
sumXY += chunkMeasurements[i].chunkDownloadTimeRelativeMS * chunkMeasurements[i].bufferLevel;
sumXSq += chunkMeasurements[i].chunkDownloadTimeRelativeMS * chunkMeasurements[i].chunkDownloadTimeRelativeMS
}
result.m = ((sumXY - sumX * sumY / N)) / (sumXSq - sumX * sumX / N)
result.b = sumY / N - result.m * sumX / N
return function (x) {
return result.m * x + result.b
}
}
function isBufferSafeAndStable(lastMeasurements) {
let isBufferSafeAndStable = true;
let lastBitrate;
const aveBufferLevelLastSegements = lastMeasurements.reduce((prev, curr) => prev + curr.bufferLevelAtSegmentEnd, 0) / lastMeasurements.length;
lastMeasurements.forEach(m => {
// inner segment buffer stability
if (Math.abs(m.bufferLevelAtSegmentEnd / m.bufferLevelAtSegmentStart) < 0.95) {
isBufferSafeAndStable = false;
}
// inter segment buffer stability
if (m.bufferLevelAtSegmentEnd / aveBufferLevelLastSegements < 0.8) {
isBufferSafeAndStable = false;
}
// representation bitrate remained at least constant
if (!lastBitrate) {
lastBitrate = m.bitrate;
} else if (lastBitrate > m.bitrate) {
isBufferSafeAndStable = false;
}
});
return isBufferSafeAndStable;
}
/**
* Based on the MPD, timing and buffer information of the last recent segments and their chunks
* the most stable download time (in milliseconds) is calculated.
* @param {*} request HTTPLoader request object
* @returns download time in milliseconds of last fetched segment
*/
function getEstimatedDownloadDurationMS(request) {
const lastMeasurement = measurements[request.mediaType].slice(-1).pop();
const lastThreeMeasurements = measurements[request.mediaType].slice(-3)
// calculate and remember the buffer level trend during the last fetched segment
const lastChunkRelativeTimeMS = lastMeasurement.chunkMeasurements.slice(-1).pop().chunkDownloadTimeRelativeMS;
lastMeasurement.bufferLevelAtSegmentStart = lastMeasurement.getEstimatedBufferLevel(lastChunkRelativeTimeMS / 2);
lastMeasurement.bufferLevelAtSegmentEnd = lastMeasurement.getEstimatedBufferLevel(lastChunkRelativeTimeMS);
const isBufferStable = isBufferSafeAndStable(lastThreeMeasurements);
const selectedOptimisticFactor = isBufferStable ? LLTM_OPTIMISTIC_ESTIMATE_FACTOR : LLTM_SEMI_OPTIMISTIC_ESTIMATE_FACTOR;
// fetch duration was longer than segment duration, but buffer was stable
if (lastMeasurement.isBufferStable && lastMeasurement.segDurationMS * LLTM_SLOW_SEGMENT_DOWNLOAD_TOLERANCE < lastMeasurement.fetchDownloadDurationMS) {
return lastMeasurement.fetchDownloadDurationMS;
}
// buffer is drying or fetch took too long
if (!isBufferStable || lastMeasurement.segDurationMS < lastMeasurement.fetchDownloadDurationMS) {
return lastMeasurement.fetchDownloadDurationMS * LLTM_SEMI_OPTIMISTIC_ESTIMATE_FACTOR;
}
// did we requested a fully available segment? -> most accurate throughput calculation
// we use adjusted availability start time to decide
// Note: this "download mode" usually happens at startup and if requests are delayed artificially
if (lastMeasurement.adjustedAvailabilityStartTimeMS <= (lastMeasurement.requestTimeMS + lastMeasurement.throughputCapacityDelayMS) - lastMeasurement.segDurationMS) {
return lastMeasurement.fetchDownloadDurationMS * LLTM_SEMI_OPTIMISTIC_ESTIMATE_FACTOR;
}
// get all chunks that have been downloaded before fetch reached bleeding live edge
// the remaining chunks loaded at production rate we will approximated
const chunkAvailablePeriod = (lastMeasurement.requestTimeMS + lastMeasurement.throughputCapacityDelayMS) - lastMeasurement.adjustedAvailabilityStartTimeMS;
let chunkBytesBBLE = 0; // BBLE -> Before bleeding live edge
let chunkDownloadtimeMSBBLE = 0;
let chunkCount = 0;
for (let index = 0; index < lastMeasurement.chunkMeasurements.length; index++) {
const chunk = lastMeasurement.chunkMeasurements[index];
if (chunkAvailablePeriod < chunkDownloadtimeMSBBLE + chunk.chunkDownloadDurationMS) {
break;
}
chunkDownloadtimeMSBBLE += chunk.chunkDownloadDurationMS;
chunkBytesBBLE += chunk.chunkBytes;
chunkCount++;
}
if (chunkAvailablePeriod < 0) {
logger.warn('request time was before adjusted availibitly start time');
}
// there have to be some chunks available (20% of max count)
// otherwise we are at bleeding live edge and the few chunks are insufficient to estimate correctly
if (chunkBytesBBLE && chunkDownloadtimeMSBBLE && chunkCount > lastMeasurement.chunkMeasurements.length * 0.2) {
const downloadThroughput = chunkBytesBBLE / chunkDownloadtimeMSBBLE; // bytes per millesecond
const estimatedDownloadtimeMS = lastMeasurement.segmentBytes / downloadThroughput;
// if real download was shorter then report this incl. semi optimistical estimate factor
if (lastMeasurement.fetchDownloadDurationMS < estimatedDownloadtimeMS) {
return lastMeasurement.fetchDownloadDurationMS * selectedOptimisticFactor;
}
return estimatedDownloadtimeMS * selectedOptimisticFactor;
}
// when we are to tight at live edge and it's stable then
// we start to optimistically estimate download time
// in such a way that a switch to next rep will be possible
// optimistical estimate: assume download was fast enough for next higher rendition
let nextHigherBitrate = lastMeasurement.bitrate;
lastMeasurement.bitrateList.some(b => {
if (b.bandwidth > lastMeasurement.bitrate) {
nextHigherBitrate = b.bandwidth;
return true;
}
});
// already highest bitrate?
if (nextHigherBitrate === lastMeasurement.bitrate) {
return lastMeasurement.fetchDownloadDurationMS * selectedOptimisticFactor;
}
return selectedOptimisticFactor * lastMeasurement.segmentBytes * 8 * 1000 / nextHigherBitrate;
}
/**
* Get calculated value for a safe artificial delay of the next request to allow to accumulate some chunks.
* This allows better line throughput measurement.
* @param {*} request
* @param {*} currentBufferLevel current buffer level in milliseconds
* @returns delay in milliseconds
*/
function getThroughputCapacityDelayMS(request, currentBufferLevelMS) {
const lastThreeMeasurements = measurements[request.mediaType] && measurements[request.mediaType].slice(-3);
if (!lastThreeMeasurements || lastThreeMeasurements.length < 3) {
return 0;
}
// in case not stable buffer, no artificially delay for the next request
if (!isBufferSafeAndStable(lastThreeMeasurements)) {
return 0;
}
// allowed artificial delay is the min of quater of buffer level in milliseconds and LLTM_MAX_DELAY_MS
return currentBufferLevelMS / 4 > LLTM_MAX_DELAY_MS ? LLTM_MAX_DELAY_MS : currentBufferLevelMS / 4;
}
/**
* Add some measurement data for bookkeeping and being able to derive decisions on estimated throughput.
* @param {*} request HTTPLoader object to get MPD and media info from
* @param {*} fetchDownloadDurationMS Duration how long the fetch actually took
* @param {*} chunkMeasurements Array containing chunk timings and buffer levels
* @param {*} requestTimeMS Timestamp at which the fetch was initiated
* @param {*} throughputCapacityDelayMS An artificial delay that was used for this request
*/
function addMeasurement(request, fetchDownloadDurationMS, chunkMeasurements, requestTimeMS, throughputCapacityDelayMS) {
if (request && request.mediaType && !measurements[request.mediaType]) {
measurements[request.mediaType] = [];
}
const bitrateEntry = request.mediaInfo.bitrateList.find(item => item.id === request.representationId);
measurements[request.mediaType].push({
index: request.index,
repId: request.representationId,
mediaType: request.mediaType,
requestTimeMS,
adjustedAvailabilityStartTimeMS: request.availabilityStartTime.getTime(),
segDurationMS: request.duration * 1000,
chunksDurationMS: chunkMeasurements.reduce((prev, curr) => prev + curr.chunkDownloadDurationMS, 0),
segmentBytes: chunkMeasurements.reduce((prev, curr) => prev + curr.chunkBytes, 0),
bitrate: bitrateEntry && bitrateEntry.bandwidth,
bitrateList: request.mediaInfo.bitrateList,
chunkMeasurements,
fetchDownloadDurationMS,
throughputCapacityDelayMS,
getEstimatedBufferLevel: createBufferLevelTrendFunction(chunkMeasurements.slice(1)) // don't use first chunk's buffer level
});
// maintain only a maximum amount of most recent measurements
if (measurements[request.mediaType].length > LLTM_MAX_MEASUREMENTS) {
measurements[request.mediaType].shift();
}
}
instance = {
setup,
addMeasurement,
getThroughputCapacityDelayMS,
getEstimatedDownloadDurationMS
};
setup()
return instance;
}
LowLatencyThroughputModel.__dashjs_factory_name = 'LowLatencyThroughputModel';
export default FactoryMaker.getSingletonFactory(LowLatencyThroughputModel);
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$( "#toc" ).toc( {
anchorName : function ( i, heading, prefix ) {
return $( heading ).attr( "id" ) || ( prefix + i );
},
selectors : "#toc-content h1,#toc-content h2,#toc-content h3,#toc-content h4",
showAndHide : false,
smoothScrolling: true
} );
$( "#main span[id^='toc']" ).addClass( "toc-shim" );
$( '.dropdown-toggle' ).dropdown();
$( "table" ).each( function () {
var $this = $( this );
$this.addClass('table');
} );
} );
</script>
<!--Navigation and Symbol Display-->
<script>
$( function () {
$( '#main' ).localScroll( {
offset : { top : 60 } //offset by the height of your header (give or take a few px, see what works for you)
} );
$( "dt.name" ).each( function () {
var $this = $( this ).find("h4");
var icon = $( "<i/>" ).addClass( "icon-plus-sign" ).addClass( "pull-right" ).addClass( "icon-white" );
var dt = $(this);
var children = dt.next( "dd" );
dt.prepend( icon ).css( {cursor : "pointer"} );
dt.addClass( "member-collapsed" ).addClass( "member" );
children.hide();
dt.children().on( "click", function () {
children = dt.next( "dd" );
children.slideToggle( "fast", function () {
if ( children.is( ":visible" ) ) {
icon.addClass( "icon-minus-sign" ).removeClass( "icon-plus-sign" ).removeClass( "icon-white" );
dt.addClass( "member-open" ).animate( "member-collapsed" );
} else {
icon.addClass( "icon-plus-sign" ).removeClass( "icon-minus-sign" ).addClass( "icon-white" );
dt.addClass( "member-collapsed" ).removeClass( "member-open" );
}
} );
} );
} );
} );
</script>
<!--Google Analytics-->
<script type="text/javascript">
$(document).ready(function() {
SearcherDisplay.init();
});
</script>
</body>
</html>