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refactor forward/backward program date time extrapolation

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This commit is contained in:
Dzianis Dashkevich 2023-07-05 19:18:01 -04:00
commit 600dff9956
1 changed files with 21 additions and 40 deletions
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61
src/parser.js
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@ -97,6 +97,8 @@ export default class Parser extends Stream {
this.parseStream = new ParseStream();
this.lineStream.pipe(this.parseStream);
this.lastProgramDateTime = null;
/* eslint-disable consistent-this */
const self = this;
/* eslint-enable consistent-this */
@ -132,7 +134,6 @@ export default class Parser extends Stream {
let lastByterangeEnd = 0;
// keep track of the last seen part's byte range end.
let lastPartByterangeEnd = 0;
let firstPdtIndex = -1;
const dateRangeTags = {};
this.on('end', () => {
@ -464,12 +465,21 @@ export default class Parser extends Stream {
currentUri.dateTimeString = entry.dateTimeString;
currentUri.dateTimeObject = entry.dateTimeObject;
const { lastProgramDateTime } = this;
// Explicitly set program date time:
currentUri.programDateTime = new Date(entry.dateTimeObject).getTime();
this.lastProgramDateTime = currentUri.programDateTime;
if (firstPdtIndex === -1) {
firstPdtIndex = this.manifest.segments.length;
this.backfillPDT_(firstPdtIndex);
// we should extrapolate Program Date Time backward only during firs program date time occurrence.
// Once we have at least one program date time point, we can always extrapolate it forward using lastProgramDateTime reference.
if (lastProgramDateTime === null) {
// Extrapolate Program Date Time backward
// Since it is first program date time occurrence we're assuming that
// all this.manifest.segments have no program date time info
this.manifest.segments.reduceRight((programDateTime, segment) => {
segment.programDateTime = programDateTime - (segment.duration * 1000);
return segment.programDateTime;
}, this.lastProgramDateTime);
}
},
targetduration() {
@ -734,9 +744,14 @@ export default class Parser extends Stream {
// reset the last byterange end as it needs to be 0 between parts
lastPartByterangeEnd = 0;
// Once we have at least one program date time, and it wasn't set explicitly we can always extrapolate it forward:
if (this.lastProgramDateTime !== null && currentUri.programDateTime === undefined) {
currentUri.programDateTime = this.lastProgramDateTime + (currentUri.duration * 1000);
this.lastProgramDateTime = currentUri.programDateTime;
}
// prepare for the next URI
currentUri = {};
this.addPDTToSegment_();
},
comment() {
// comments are not important for playback
@ -788,6 +803,7 @@ export default class Parser extends Stream {
// flush any buffered input
this.lineStream.push('\n');
this.lastProgramDateTime = null;
this.trigger('end');
}
/**
@ -812,39 +828,4 @@ export default class Parser extends Stream {
addTagMapper(options) {
this.parseStream.addTagMapper(options);
}
/**
* Backfills missing PDT values when the first EXT-X-PROGRAM-DATE-TIME tag in
* the Playlist appears after one or more segments
*/
backfillPDT_(firstPdtIndex) {
if (!firstPdtIndex > 0) {
return;
}
let segmentWithPdt = this.manifest.segments[firstPdtIndex - 1];
segmentWithPdt.programDateTime = segmentWithPdt.programDateTime || this.lastProgramDateTime;
for (let index = firstPdtIndex - 1; index > -1; index--) {
const segment = this.manifest.segments[index];
segment.programDateTime = segmentWithPdt.programDateTime - segment.duration * 1000;
segmentWithPdt = segment;
}
}
/**
* Adds PDT to values to segments that do not contain explicit PDT tags
*
*/
addPDTToSegment_() {
if (!this.lastProgramDateTime || !this.manifest.segments.length > 1) {
return;
}
const segments = this.manifest.segments;
const currentSegment = segments[this.manifest.segments.length - 1];
const prevSegment = segments[this.manifest.segments.length - 2];
if (segments.length > 0 && !currentSegment.dateTimeString && !currentSegment.programDateTime) {
currentSegment.programDateTime = prevSegment.programDateTime + (currentSegment.duration * 1000);
}
}
}