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fix(HLS): support discontinuities in segments mode (#5102)
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@swac @joeyparrish
swac authored and joeyparrish committed Apr 26, 2023
1 parent ca118df commit cfcca8e
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Showing 6 changed files with 141 additions and 11 deletions.
9 changes: 7 additions & 2 deletions lib/hls/hls_parser.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2371,13 +2371,15 @@ shaka.hls.HlsParser = class {
* @param {!Map.<string, string>} variables
* @param {string} absoluteMediaPlaylistUri
* @param {string} type
* @param {number} timestampOffset
* @param {shaka.extern.HlsAes128Key=} hlsAes128Key
* @return {shaka.media.SegmentReference}
* @private
*/
createSegmentReference_(
initSegmentReference, previousReference, hlsSegment, startTime,
variables, absoluteMediaPlaylistUri, type, hlsAes128Key) {
variables, absoluteMediaPlaylistUri, type, timestampOffset,
hlsAes128Key) {
const tags = hlsSegment.tags;
const absoluteSegmentUri = this.variableSubstitution_(
hlsSegment.absoluteUri, variables);
Expand Down Expand Up @@ -2547,7 +2549,7 @@ shaka.hls.HlsParser = class {
startByte,
endByte,
initSegmentReference,
/* timestampOffset= */ 0, // This value is ignored in sequence mode.
timestampOffset, // This value is ignored in sequence mode.
/* appendWindowStart= */ 0,
/* appendWindowEnd= */ Infinity,
partialSegmentRefs,
Expand Down Expand Up @@ -2632,6 +2634,7 @@ shaka.hls.HlsParser = class {
const references = [];

let previousReference = null;
let lastDiscontinuityStartTime = firstStartTime;

for (let i = 0; i < hlsSegments.length; i++) {
const item = hlsSegments[i];
Expand All @@ -2643,6 +2646,7 @@ shaka.hls.HlsParser = class {
item.tags, 'EXT-X-DISCONTINUITY');
if (discontinuityTag) {
discontinuitySequence++;
lastDiscontinuityStartTime = startTime;
}

// Apply new AES-128 tags as you see them, keeping a running total.
Expand Down Expand Up @@ -2681,6 +2685,7 @@ shaka.hls.HlsParser = class {
variables,
playlist.absoluteUri,
type,
lastDiscontinuityStartTime,
hlsAes128Key);
previousReference = reference;

Expand Down
4 changes: 0 additions & 4 deletions lib/media/media_source_engine.js
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Expand Up @@ -952,7 +952,6 @@ shaka.media.MediaSourceEngine = class {

/**
* Adjust timestamp offset to maintain AV sync across discontinuities.
* Only used in sequence mode.
*
* @param {shaka.util.ManifestParserUtils.ContentType} contentType
* @param {number} timestampOffset
Expand All @@ -961,9 +960,6 @@ shaka.media.MediaSourceEngine = class {
async resync(contentType, timestampOffset) {
const ContentType = shaka.util.ManifestParserUtils.ContentType;

goog.asserts.assert(this.sequenceMode_,
'resync only used with sequence mode!');

if (contentType == ContentType.TEXT) {
// This operation is for audio and video only.
return;
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5 changes: 3 additions & 2 deletions lib/media/segment_reference.js
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Expand Up @@ -144,8 +144,9 @@ shaka.media.SegmentReference = class {
* minus the first segment's tfdt box's 'baseMediaDecodeTime' field (after
* it has been converted to seconds).
* <br>
* For HLS, this value should be 0 to keep the presentation time at the most
* recent discontinuity minus the corresponding media time.
* For HLS, this value should be the start time of the most recent
* discontinuity, or 0 if there is no preceding discontinuity. Only used
* in segments mode.
* @param {number} appendWindowStart
* The start of the append window for this reference, relative to the
* presentation. Any content from before this time will be removed by
Expand Down
18 changes: 15 additions & 3 deletions lib/media/streaming_engine.js
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Expand Up @@ -1675,19 +1675,31 @@ shaka.media.StreamingEngine = class {
}
}

const lastDiscontinuitySequence =
mediaState.lastSegmentReference ?
mediaState.lastSegmentReference.discontinuitySequence : null;
if (this.manifest_.sequenceMode) {
// Across discontinuity bounds, we should resync timestamps for
// sequence mode playbacks. The next segment appended should
// land at its theoretical timestamp from the segment index.
const lastDiscontinuitySequence =
mediaState.lastSegmentReference ?
mediaState.lastSegmentReference.discontinuitySequence : null;
if (reference.discontinuitySequence != lastDiscontinuitySequence ||
mediaState.needsResync) {
mediaState.needsResync = false;
operations.push(this.playerInterface_.mediaSourceEngine.resync(
mediaState.type, reference.startTime));
}
} else {
// In segments mode, we need to resync to set the timestampOffset
// to the start of the current discontinuity sequence. This is
// because individual discontinuity sequences may have internal
// timestamps that overlap, so we adjust the timestampOffset to avoid
// having the SourceBuffer get overwritten.
if (reference.discontinuitySequence != lastDiscontinuitySequence) {
operations.push(
this.playerInterface_.mediaSourceEngine.resync(
mediaState.type,
reference.timestampOffset));
}
}

await Promise.all(operations);
Expand Down
112 changes: 112 additions & 0 deletions test/hls/hls_parser_unit.js
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Expand Up @@ -987,6 +987,118 @@ describe('HlsParser', () => {
await testHlsParser(master, media, manifest);
});

it('parses discontinuity tags', async () => {
const master = [
'#EXTM3U\n',
'#EXT-X-STREAM-INF:BANDWIDTH=2000000,CODECS="avc1"\n',
'video\n',
].join('');

const media = [
'#EXTM3U\n',
'#EXT-X-VERSION:3\n',
'#EXT-X-TARGETDURATION:5\n',
'#EXT-X-MEDIA-SEQUENCE:0\n',
'#EXTINF:3,\n',
'clip0-video-0.ts\n',
'#EXTINF:1,\n',
'clip0-video-1.ts\n',
'#EXT-X-DISCONTINUITY\n',
'#EXTINF:2,\n',
'clip1-video-1.ts\n',
'#EXTINF:3,\n',
'clip1-video-2.ts\n',
'#EXT-X-DISCONTINUITY\n',
'#EXTINF:1,\n',
'media-clip2-video-0.ts\n',
'#EXTINF:1,\n',
'media-clip2-video-1.ts\n',
'#EXT-X-DISCONTINUITY\n',
'#EXTINF:4,\n',
'media-clip3-video-1.ts\n',
'#EXT-X-ENDLIST\n',
].join('');

fakeNetEngine
.setResponseText('test:/master', master)
.setResponseText('test:/video', media);

const manifest = await parser.start('test:/master', playerInterface);
await manifest.variants[0].video.createSegmentIndex();

const segmentIndex = manifest.variants[0].video.segmentIndex;
const references = [];

for (let i = 0; i < 7; i++) {
references.push(segmentIndex.get(i));
}

expect(references[0].discontinuitySequence).toBe(0);
expect(references[1].discontinuitySequence).toBe(0);
expect(references[2].discontinuitySequence).toBe(1);
expect(references[3].discontinuitySequence).toBe(1);
expect(references[4].discontinuitySequence).toBe(2);
expect(references[5].discontinuitySequence).toBe(2);
expect(references[6].discontinuitySequence).toBe(3);
});

it('sets reference timetampOffset based on discontinuity start time',
async () => {
const master = [
'#EXTM3U\n',
'#EXT-X-STREAM-INF:BANDWIDTH=2000000,CODECS="avc1"\n',
'video\n',
].join('');

const media = [
'#EXTM3U\n',
'#EXT-X-VERSION:3\n',
'#EXT-X-TARGETDURATION:5\n',
'#EXT-X-MEDIA-SEQUENCE:0\n',
'#EXTINF:3,\n',
'clip0-video-0.ts\n',
'#EXTINF:1,\n',
'clip0-video-1.ts\n',
'#EXT-X-DISCONTINUITY\n',
'#EXTINF:2,\n',
'clip1-video-1.ts\n',
'#EXTINF:3,\n',
'clip1-video-2.ts\n',
'#EXT-X-DISCONTINUITY\n',
'#EXTINF:1,\n',
'media-clip2-video-0.ts\n',
'#EXTINF:1,\n',
'media-clip2-video-1.ts\n',
'#EXT-X-DISCONTINUITY\n',
'#EXTINF:4,\n',
'media-clip3-video-1.ts\n',
'#EXT-X-ENDLIST\n',
].join('');

fakeNetEngine
.setResponseText('test:/master', master)
.setResponseText('test:/video', media);

const manifest = await parser.start('test:/master', playerInterface);
await manifest.variants[0].video.createSegmentIndex();

const segmentIndex = manifest.variants[0].video.segmentIndex;
const references = [];

for (let i = 0; i < 7; i++) {
references.push(segmentIndex.get(i));
}

expect(references[0].timestampOffset).toBe(0);
expect(references[1].timestampOffset).toBe(0);
expect(references[2].timestampOffset).toBe(4);
expect(references[3].timestampOffset).toBe(4);
expect(references[4].timestampOffset).toBe(9);
expect(references[5].timestampOffset).toBe(9);
expect(references[6].timestampOffset).toBe(11);
},
);

it('parses characteristics from audio tags', async () => {
const master = [
'#EXTM3U\n',
Expand Down
4 changes: 4 additions & 0 deletions test/test/util/fake_media_source_engine.js
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Original file line number Diff line number Diff line change
Expand Up @@ -136,6 +136,10 @@ shaka.test.FakeMediaSourceEngine = class {
/** @type {!jasmine.Spy} */
this.updateLcevcDil =
jasmine.createSpy('updateLcevcDil').and.stub();

/** @type {!jasmine.Spy} */
this.resync=
jasmine.createSpy('resync').and.stub();
}

/** @override */
Expand Down

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