shaka-player
Version:
DASH/EME video player library
432 lines (377 loc) • 12.9 kB
JavaScript
/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
goog.provide('shaka.text.Mp4VttParser');
goog.require('goog.asserts');
goog.require('shaka.log');
goog.require('shaka.text.Cue');
goog.require('shaka.text.TextEngine');
goog.require('shaka.text.VttTextParser');
goog.require('shaka.util.DataViewReader');
goog.require('shaka.util.Error');
goog.require('shaka.util.Functional');
goog.require('shaka.util.Iterables');
goog.require('shaka.util.Mp4Parser');
goog.require('shaka.util.StringUtils');
goog.require('shaka.util.TextParser');
/**
* @implements {shaka.extern.TextParser}
* @export
*/
shaka.text.Mp4VttParser = class {
/** */
constructor() {
/**
* The current time scale used by the VTT parser.
*
* @type {?number}
* @private
*/
this.timescale_ = null;
}
/**
* @override
* @export
*/
parseInit(data) {
const Mp4Parser = shaka.util.Mp4Parser;
let sawWVTT = false;
new Mp4Parser()
.box('moov', Mp4Parser.children)
.box('trak', Mp4Parser.children)
.box('mdia', Mp4Parser.children)
.fullBox('mdhd', (box) => {
goog.asserts.assert(
box.version == 0 || box.version == 1,
'MDHD version can only be 0 or 1');
if (box.version == 0) {
box.reader.skip(4); // Skip "creation_time".
box.reader.skip(4); // Skip "modification_time".
this.timescale_ = box.reader.readUint32();
box.reader.skip(4); // Skip "duration".
} else {
box.reader.skip(8); // Skip "creation_time".
box.reader.skip(8); // Skip "modification_time".
this.timescale_ = box.reader.readUint32();
box.reader.skip(8); // Skip "duration".
}
box.reader.skip(4); // Skip "pad", "language", and "pre-defined".
})
.box('minf', Mp4Parser.children)
.box('stbl', Mp4Parser.children)
.fullBox('stsd', Mp4Parser.sampleDescription)
.box('wvtt', (box) => {
// A valid vtt init segment, though we have no actual subtitles yet.
sawWVTT = true;
}).parse(data);
if (!this.timescale_) {
// Missing timescale for VTT content. It should be located in the MDHD.
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.INVALID_MP4_VTT);
}
if (!sawWVTT) {
// A WVTT box should have been seen (a valid vtt init segment with no
// actual subtitles).
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.INVALID_MP4_VTT);
}
}
/**
* @override
* @export
*/
parseMedia(data, time) {
if (!this.timescale_) {
// Missing timescale for VTT content. We should have seen the init
// segment.
shaka.log.error('No init segment for MP4+VTT!');
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.INVALID_MP4_VTT);
}
const Mp4VttParser = shaka.text.Mp4VttParser;
const Mp4Parser = shaka.util.Mp4Parser;
let baseTime = 0;
/** @type {!Array.<shaka.text.Mp4VttParser.TimeSegment>} */
let presentations = [];
/** @type {!Uint8Array} */
let rawPayload;
/** @type {!Array.<shaka.text.Cue>} */
const cues = [];
let sawTFDT = false;
let sawTRUN = false;
let sawMDAT = false;
let defaultDuration = null;
const parser = new Mp4Parser()
.box('moof', Mp4Parser.children)
.box('traf', Mp4Parser.children)
.fullBox('tfdt', (box) => {
sawTFDT = true;
goog.asserts.assert(
box.version == 0 || box.version == 1,
'TFDT version can only be 0 or 1');
baseTime = (box.version == 0) ? box.reader.readUint32() :
box.reader.readUint64();
})
.fullBox('tfhd', (box) => {
goog.asserts.assert(
box.flags != null,
'A TFHD box should have a valid flags value');
defaultDuration = Mp4VttParser.parseTFHD_(box.flags, box.reader);
})
.fullBox('trun', (box) => {
sawTRUN = true;
goog.asserts.assert(
box.version != null,
'A TRUN box should have a valid version value');
goog.asserts.assert(
box.flags != null,
'A TRUN box should have a valid flags value');
presentations =
Mp4VttParser.parseTRUN_(box.version, box.flags, box.reader);
})
.box('mdat', Mp4Parser.allData((data) => {
goog.asserts.assert(
!sawMDAT,
'VTT cues in mp4 with multiple MDAT are not currently supported');
sawMDAT = true;
rawPayload = data;
}));
parser.parse(data, /* partialOkay= */ false);
if (!sawMDAT && !sawTFDT && !sawTRUN) {
// A required box is missing.
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.INVALID_MP4_VTT);
}
let currentTime = baseTime;
/** @type {!shaka.util.DataViewReader} */
const reader = new shaka.util.DataViewReader(
rawPayload, shaka.util.DataViewReader.Endianness.BIG_ENDIAN);
for (const presentation of presentations) {
// If one presentation corresponds to multiple payloads, it is assumed
// that all of those payloads have the same start time and duration.
const duration = presentation.duration || defaultDuration;
const startTime = presentation.timeOffset ?
baseTime + presentation.timeOffset :
currentTime;
currentTime = startTime + (duration || 0);
// Read samples until it adds up to the given size.
let totalSize = 0;
do {
// Read the payload size.
const payloadSize = reader.readUint32();
totalSize += payloadSize;
// Skip the type.
const payloadType = reader.readUint32();
const payloadName = shaka.util.Mp4Parser.typeToString(payloadType);
// Read the data payload.
/** @type {Uint8Array} */
let payload = null;
if (payloadName == 'vttc') {
if (payloadSize > 8) {
payload = reader.readBytes(payloadSize - 8);
}
} else if (payloadName == 'vtte') {
// It's a vtte, which is a vtt cue that is empty. Ignore any data that
// does exist.
reader.skip(payloadSize - 8);
} else {
shaka.log.error('Unknown box ' + payloadName + '! Skipping!');
reader.skip(payloadSize - 8);
}
if (duration) {
if (payload) {
goog.asserts.assert(
this.timescale_ != null, 'Timescale should not be null!');
const cue = shaka.text.Mp4VttParser.parseVTTC_(
payload,
time.periodStart + startTime / this.timescale_,
time.periodStart + currentTime / this.timescale_);
cues.push(cue);
}
} else {
shaka.log.error(
'WVTT sample duration unknown, and no default found!');
}
goog.asserts.assert(
!presentation.sampleSize || totalSize <= presentation.sampleSize,
'The samples do not fit evenly into the sample sizes given in ' +
'the TRUN box!');
// If no sampleSize was specified, it's assumed that this presentation
// corresponds to only a single cue.
} while (presentation.sampleSize &&
(totalSize < presentation.sampleSize));
}
goog.asserts.assert(
!reader.hasMoreData(),
'MDAT which contain VTT cues and non-VTT data are not currently ' +
'supported!');
return /** @type {!Array.<!shaka.extern.Cue>} */ (
cues.filter(shaka.util.Functional.isNotNull));
}
/**
* @param {number} flags
* @param {!shaka.util.DataViewReader} reader
* @return {?number} The default_sample_duration field, if present.
* @private
*/
static parseTFHD_(flags, reader) {
// Skip "track_ID".
reader.skip(4);
// Skip "base_data_offset" if present.
if (flags & 0x000001) {
reader.skip(8);
}
// Skip "sample_description_index" if present.
if (flags & 0x000002) {
reader.skip(4);
}
// Read and return "default_sample_duration" if present.
if (flags & 0x000008) {
return reader.readUint32();
}
// There is no "default_sample_duration".
return null;
}
/**
* @param {number} version
* @param {number} flags
* @param {!shaka.util.DataViewReader} reader
* @return {!Array.<shaka.text.Mp4VttParser.TimeSegment>}
* @private
*/
static parseTRUN_(version, flags, reader) {
const sampleCount = reader.readUint32();
// Skip "data_offset" if present.
if (flags & 0x000001) {
reader.skip(4);
}
// Skip "first_sample_flags" if present.
if (flags & 0x000004) {
reader.skip(4);
}
const samples = [];
for (const _ of shaka.util.Iterables.range(sampleCount)) {
shaka.util.Functional.ignored(_);
/** @type {shaka.text.Mp4VttParser.TimeSegment} */
const sample = {
duration: null,
sampleSize: null,
timeOffset: null,
};
// Read "sample duration" if present.
if (flags & 0x000100) {
sample.duration = reader.readUint32();
}
// Read "sample_size" if present.
if (flags & 0x000200) {
sample.sampleSize = reader.readUint32();
}
// Skip "sample_flags" if present.
if (flags & 0x000400) {
reader.skip(4);
}
// Read "sample_time_offset" if present.
if (flags & 0x000800) {
sample.timeOffset = version == 0 ?
reader.readUint32() :
reader.readInt32();
}
samples.push(sample);
}
return samples;
}
/**
* Parses a vttc box into a cue.
*
* @param {!Uint8Array} data
* @param {number} startTime
* @param {number} endTime
* @return {shaka.text.Cue}
* @private
*/
static parseVTTC_(data, startTime, endTime) {
let payload;
let id;
let settings;
new shaka.util.Mp4Parser()
.box('payl', shaka.util.Mp4Parser.allData((data) => {
payload = shaka.util.StringUtils.fromUTF8(data);
}))
.box('iden', shaka.util.Mp4Parser.allData((data) => {
id = shaka.util.StringUtils.fromUTF8(data);
}))
.box('sttg', shaka.util.Mp4Parser.allData((data) => {
settings = shaka.util.StringUtils.fromUTF8(data);
}))
.parse(data);
if (payload) {
return shaka.text.Mp4VttParser.assembleCue_(
payload, id, settings, startTime, endTime);
} else {
return null;
}
}
/**
* Take the individual components that make a cue and create a vttc cue.
*
* @param {string} payload
* @param {?string} id
* @param {?string} settings
* @param {number} startTime
* @param {number} endTime
* @return {!shaka.text.Cue}
* @private
*/
static assembleCue_(payload, id, settings, startTime, endTime) {
const cue = new shaka.text.Cue(startTime, endTime, payload);
if (id) {
cue.id = id;
}
if (settings) {
const parser = new shaka.util.TextParser(settings);
let word = parser.readWord();
while (word) {
// TODO: Check WebVTTConfigurationBox for region info.
if (!shaka.text.VttTextParser.parseCueSetting(
cue, word, /* VTTRegions= */[])) {
shaka.log.warning(
'VTT parser encountered an invalid VTT setting: ', word,
' The setting will be ignored.');
}
parser.skipWhitespace();
word = parser.readWord();
}
}
return cue;
}
};
/**
* @typedef {{
* duration: ?number,
* sampleSize: ?number,
* timeOffset: ?number
* }}
*
* @property {?number} duration
* The length of the segment in timescale units.
* @property {?number} sampleSize
* The size of the segment in bytes.
* @property {?number} timeOffset
* The time since the start of the segment in timescale units. Time
* offset is based of the start of the segment. If this value is
* missing, the accumated durations preceeding this time segment will
* be used to create the start time.
*/
shaka.text.Mp4VttParser.TimeSegment;
shaka.text.TextEngine.registerParser(
'application/mp4; codecs="wvtt"', () => new shaka.text.Mp4VttParser());