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Make partial segment requests in HLS parser
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This speeds up HLS stream startup significantly for servers that
permit this kind of request, and falls back to full segments for
servers that do not.

Closes #1106

Change-Id: I96bc7f0df0fb84b75f3a3fe43476ba0ba5fc2264
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@joeyparrish
joeyparrish committed Nov 7, 2017
1 parent bde4c45 commit a93455a
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Showing 7 changed files with 125 additions and 52 deletions.
109 changes: 79 additions & 30 deletions lib/hls/hls_parser.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1216,6 +1216,54 @@ shaka.hls.HlsParser.prototype.createSegments_ =
};


/**
* Try to fetch a partial segment, and fall back to a full segment if we have
* to.
*
* @param {!shaka.media.SegmentReference} segmentRef
* @return {!Promise.<shakaExtern.Response>}
* @throws {shaka.util.Error}
* @private
*/
shaka.hls.HlsParser.prototype.fetchPartialSegment_ = function(segmentRef) {
var networkingEngine = this.playerInterface_.networkingEngine;
var requestType = shaka.net.NetworkingEngine.RequestType.SEGMENT;
var request = shaka.net.NetworkingEngine.makeRequest(
segmentRef.getUris(), this.config_.retryParameters);

// Try to avoid fetching the entire segment, which can be quite large.
var partialSegmentHeaders = {};
var startByte = segmentRef.startByte;
var partialEndByte = startByte + shaka.hls.HlsParser.PARTIAL_SEGMENT_SIZE_;
partialSegmentHeaders['Range'] = 'bytes=' + startByte + '-' + partialEndByte;

// Prepare a fallback to the entire segment.
var fullSegmentHeaders = {};
if ((startByte != 0) || (segmentRef.endByte != null)) {
var range = 'bytes=' + startByte + '-';
if (segmentRef.endByte != null) range += segmentRef.endByte;

fullSegmentHeaders['Range'] = range;
}

// Try a partial request first.
request.headers = partialSegmentHeaders;
return networkingEngine.request(requestType, request).catch(function(error) {
// The partial request may fail for a number of reasons.
// Some servers do not support Range requests, and others do not support the
// OPTIONS request which must be made before any cross-origin Range request.
// Since this fallback is expensive, warn the app developer.
shaka.log.alwaysWarn('Unable to fetch a partial HLS segment! ' +
'Falling back to a full segment request, ' +
'which is expensive! Your server should support ' +
'Range requests and CORS preflights.',
request.uris[0]);
request.headers = fullSegmentHeaders;
return networkingEngine.request(requestType, request);
});
};


/**
* Gets start time of a segment from the existing manifest (if possible) or by
* downloading it and parsing it otherwise.
Expand Down Expand Up @@ -1249,37 +1297,25 @@ shaka.hls.HlsParser.prototype.getStartTime_ =
shaka.log.debug('Unable to find segment start time in previous manifest!');
}

// TODO: try fetching part of the segment, to speed up start time deduction
shaka.log.v1('Fetching segment to find start time');
var requestType = shaka.net.NetworkingEngine.RequestType.SEGMENT;
var request = shaka.net.NetworkingEngine.makeRequest(
segmentRef.getUris(), this.config_.retryParameters);

if ((segmentRef.startByte != 0) || (segmentRef.endByte != null)) {
var range = 'bytes=' + segmentRef.startByte + '-';
if (segmentRef.endByte != null) range += segmentRef.endByte;
request.headers['Range'] = range;
}

return this.playerInterface_.networkingEngine.request(requestType, request)
.then(function(response) {
if (mimeType == 'video/mp4' || mimeType == 'audio/mp4') {
return this.getStartTimeFromMp4Segment_(response.data);
} else if (mimeType == 'video/mp2t') {
return this.getStartTimeFromTsSegment_(response.data);
} else if (mimeType == 'application/mp4' ||
mimeType.indexOf('text/') == 0) {
return this.getStartTimeFromTextSegment_(
mimeType, codecs, response.data);
} else {
// TODO: Parse WebM?
// TODO: Parse raw AAC?
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.MANIFEST,
shaka.util.Error.Code.HLS_COULD_NOT_PARSE_SEGMENT_START_TIME);
}
}.bind(this));
return this.fetchPartialSegment_(segmentRef).then(function(response) {
if (mimeType == 'video/mp4' || mimeType == 'audio/mp4') {
return this.getStartTimeFromMp4Segment_(response.data);
} else if (mimeType == 'video/mp2t') {
return this.getStartTimeFromTsSegment_(response.data);
} else if (mimeType == 'application/mp4' ||
mimeType.indexOf('text/') == 0) {
return this.getStartTimeFromTextSegment_(
mimeType, codecs, response.data);
} else {
// TODO: Parse WebM?
// TODO: Parse raw AAC?
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.MANIFEST,
shaka.util.Error.Code.HLS_COULD_NOT_PARSE_SEGMENT_START_TIME);
}
}.bind(this));
};


Expand Down Expand Up @@ -1307,6 +1343,7 @@ shaka.hls.HlsParser.prototype.getStartTimeFromMp4Segment_ = function(data) {
box.reader.readUint64();
startTime = baseTime / shaka.hls.HlsParser.TS_TIMESCALE_;
parsed = true;
box.parser.stop();
}).parse(data);

if (!parsed) {
Expand Down Expand Up @@ -1930,6 +1967,18 @@ shaka.hls.HlsParser.TS_TIMESCALE_ = 90000;
// TODO: Consider extracting this from the MP4 instead of assuming a
// TS-compatible timescale in fMP4 HLS content.


/**
* The amount of data from the start of a segment we will try to fetch when we
* need to know the segment start time. This allows us to avoid fetching the
* entire segment in many cases.
*
* @const {number}
* @private
*/
shaka.hls.HlsParser.PARTIAL_SEGMENT_SIZE_ = 1024;


shaka.media.ManifestParser.registerParserByExtension(
'm3u8', shaka.hls.HlsParser);
shaka.media.ManifestParser.registerParserByMime(
Expand Down
1 change: 1 addition & 0 deletions lib/media/mp4_segment_index_parser.js
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Original file line number Diff line number Diff line change
Expand Up @@ -161,5 +161,6 @@ shaka.media.Mp4SegmentIndexParser.parseSIDX_ = function(
startByte += referenceSize;
}

box.parser.stop();
return references;
};
2 changes: 2 additions & 0 deletions lib/media/streaming_engine.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1657,6 +1657,8 @@ shaka.media.StreamingEngine.prototype.parseEMSG_ = function(
var event = new shaka.util.FakeEvent('emsg', {'detail': emsg});
this.playerInterface_.onEvent(event);
}

box.parser.stop();
};


Expand Down
1 change: 1 addition & 0 deletions lib/text/mp4_ttml_parser.js
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Original file line number Diff line number Diff line change
Expand Up @@ -53,6 +53,7 @@ shaka.text.Mp4TtmlParser.prototype.parseInit = function(data) {
.fullBox('stsd', Mp4Parser.sampleDescription)
.box('stpp', function(box) {
sawSTPP = true;
box.parser.stop();
}).parse(data);

if (!sawSTPP) {
Expand Down
29 changes: 19 additions & 10 deletions lib/util/mp4_parser.js
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Original file line number Diff line number Diff line change
Expand Up @@ -29,17 +29,14 @@ goog.require('shaka.util.DataViewReader');
* @export
*/
shaka.util.Mp4Parser = function() {
/**
* @type {!Object.<number, shaka.util.Mp4Parser.BoxType_>}
* @private
*/
/** @private {!Object.<number, shaka.util.Mp4Parser.BoxType_>} */
this.headers_ = [];

/**
* @type {!Object.<number, !shaka.util.Mp4Parser.CallbackType>}
* @private
*/
/** @private {!Object.<number, !shaka.util.Mp4Parser.CallbackType>} */
this.boxDefinitions_ = [];

/** @private {boolean} */
this.done_ = false;
};


Expand Down Expand Up @@ -126,6 +123,17 @@ shaka.util.Mp4Parser.prototype.fullBox = function(type, definition) {
};


/**
* Stop parsing. Useful for extracting information from partial segments and
* avoiding an out-of-bounds error once you find what you are looking for.
*
* @export
*/
shaka.util.Mp4Parser.prototype.stop = function() {
this.done_ = true;
};


/**
* Parse the given data using the added callbacks.
*
Expand All @@ -138,7 +146,8 @@ shaka.util.Mp4Parser.prototype.parse = function(data) {
new DataView(wrapped.buffer, wrapped.byteOffset, wrapped.byteLength),
shaka.util.DataViewReader.Endianness.BIG_ENDIAN);

while (reader.hasMoreData()) {
this.done_ = false;
while (reader.hasMoreData() && !this.done_) {
this.parseNext(0, reader);
}
};
Expand Down Expand Up @@ -215,7 +224,7 @@ shaka.util.Mp4Parser.prototype.parseNext = function(absStart, reader) {
* @export
*/
shaka.util.Mp4Parser.children = function(box) {
while (box.reader.hasMoreData()) {
while (box.reader.hasMoreData() && !box.parser.done_) {
box.parser.parseNext(box.start, box.reader);
}
};
Expand Down
7 changes: 5 additions & 2 deletions test/hls/hls_live_unit.js
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Original file line number Diff line number Diff line change
Expand Up @@ -515,6 +515,9 @@ describe('HlsParser live', function() {
});

it('gets start time of segments with byte range', function(done) {
// Nit: this value is an implementation detail of the fix for #1106
var partialEndByte = expectedStartByte + 1024;

fakeNetEngine.setResponseMap({
'test:/master': toUTF8(master),
'test:/video': toUTF8(mediaWithByteRange),
Expand All @@ -528,7 +531,7 @@ describe('HlsParser live', function() {
segmentDataStartTime + 2 /* end */,
'' /* baseUri */,
expectedStartByte,
expectedEndByte);
expectedEndByte); // Complete segment reference

parser.start('test:/master', playerInterface).then(function(manifest) {
var video = manifest.periods[0].variants[0].video;
Expand All @@ -539,7 +542,7 @@ describe('HlsParser live', function() {
fakeNetEngine.expectRangeRequest(
'test:/main.mp4',
expectedStartByte,
expectedEndByte);
partialEndByte); // Partial segment request
}).catch(fail).then(done);

shaka.polyfill.Promise.flush();
Expand Down
28 changes: 18 additions & 10 deletions test/hls/hls_parser_unit.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1305,6 +1305,8 @@ describe('HlsParser', function() {
// constructing references. Here it is covered incidentally.
var expectedStartByte = 616;
var expectedEndByte = 121705;
// Nit: this value is an implementation detail of the fix for #1106
var partialEndByte = expectedStartByte + 1024;

beforeEach(function() {
// TODO: use StreamGenerator?
Expand Down Expand Up @@ -1361,7 +1363,7 @@ describe('HlsParser', function() {
fakeNetEngine.expectRangeRequest(
'test:/main.mp4',
expectedStartByte,
expectedEndByte);
partialEndByte);

// In VOD content, we set the presentationTimeOffset to align the
// content to presentation time 0.
Expand All @@ -1387,15 +1389,21 @@ describe('HlsParser', function() {
expectedStartByte,
expectedEndByte);

parser.start('test:/master', playerInterface)
.then(function(manifest) {
var video = manifest.periods[0].variants[0].video;
ManifestParser.verifySegmentIndex(video, [ref]);
// In VOD content, we set the presentationTimeOffset to align the
// content to presentation time 0.
expect(video.presentationTimeOffset)
.toEqual(segmentDataStartTime);
}).catch(fail).then(done);
parser.start('test:/master', playerInterface).then(function(manifest) {
var video = manifest.periods[0].variants[0].video;
ManifestParser.verifySegmentIndex(video, [ref]);

// Make sure the segment data was fetched with the correct byte
// range.
fakeNetEngine.expectRangeRequest(
'test:/main.ts',
expectedStartByte,
partialEndByte);

// In VOD content, we set the presentationTimeOffset to align the
// content to presentation time 0.
expect(video.presentationTimeOffset).toEqual(segmentDataStartTime);
}).catch(fail).then(done);
});

it('sets duration with respect to presentation offset', function(done) {
Expand Down

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