shaka-player
Version:
DASH/EME video player library
450 lines (399 loc) • 13.4 kB
JavaScript
/*! @license
* Shaka Player
* Copyright 2016 Google LLC
* SPDX-License-Identifier: Apache-2.0
*/
goog.provide('shaka.text.VttTextParser');
goog.require('goog.asserts');
goog.require('shaka.log');
goog.require('shaka.text.Cue');
goog.require('shaka.text.CueRegion');
goog.require('shaka.text.TextEngine');
goog.require('shaka.util.Error');
goog.require('shaka.util.StringUtils');
goog.require('shaka.util.TextParser');
/**
* @implements {shaka.extern.TextParser}
* @export
*/
shaka.text.VttTextParser = class {
/**
* @override
* @export
*/
parseInit(data) {
goog.asserts.assert(false, 'VTT does not have init segments');
}
/**
* @override
* @export
*/
parseMedia(data, time) {
const VttTextParser = shaka.text.VttTextParser;
// Get the input as a string. Normalize newlines to \n.
let str = shaka.util.StringUtils.fromUTF8(data);
str = str.replace(/\r\n|\r(?=[^\n]|$)/gm, '\n');
const blocks = str.split(/\n{2,}/m);
if (!/^WEBVTT($|[ \t\n])/m.test(blocks[0])) {
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.INVALID_TEXT_HEADER);
}
// NOTE: "periodStart" is the timestamp offset applied via TextEngine.
// It is no longer closely tied to periods, but the name stuck around.
let offset = time.periodStart;
if (blocks[0].includes('X-TIMESTAMP-MAP')) {
// https://bit.ly/2K92l7y
// The 'X-TIMESTAMP-MAP' header is used in HLS to align text with
// the rest of the media.
// The header format is 'X-TIMESTAMP-MAP=MPEGTS:n,LOCAL:m'
// (the attributes can go in any order)
// where n is MPEG-2 time and m is cue time it maps to.
// For example 'X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000'
// means an offset of 10 seconds
// 900000/MPEG_TIMESCALE - cue time.
const cueTimeMatch =
blocks[0].match(/LOCAL:((?:(\d{1,}):)?(\d{2}):(\d{2})\.(\d{3}))/m);
const mpegTimeMatch = blocks[0].match(/MPEGTS:(\d+)/m);
if (cueTimeMatch && mpegTimeMatch) {
const parser = new shaka.util.TextParser(cueTimeMatch[1]);
const cueTime = shaka.text.VttTextParser.parseTime_(parser);
if (cueTime == null) {
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.INVALID_TEXT_HEADER);
}
let mpegTime = Number(mpegTimeMatch[1]);
const mpegTimescale = shaka.text.VttTextParser.MPEG_TIMESCALE_;
const rolloverSeconds =
shaka.text.VttTextParser.TS_ROLLOVER_ / mpegTimescale;
let segmentStart = time.segmentStart;
while (segmentStart >= rolloverSeconds) {
segmentStart -= rolloverSeconds;
mpegTime += shaka.text.VttTextParser.TS_ROLLOVER_;
}
// Apple-encoded HLS content uses absolute timestamps, so assume the
// presence of the map tag means the content uses absolute timestamps.
offset = time.periodStart + mpegTime / mpegTimescale - cueTime;
}
}
// Parse VTT regions.
/* !Array.<!shaka.extern.CueRegion> */
const regions = [];
for (const line of blocks[0].split('\n')) {
if (/^Region:/.test(line)) {
const region = VttTextParser.parseRegion_(line);
regions.push(region);
}
}
// Parse cues.
const ret = [];
for (const block of blocks.slice(1)) {
const lines = block.split('\n');
const cue = VttTextParser.parseCue_(lines, offset, regions);
if (cue) {
ret.push(cue);
}
}
return ret;
}
/**
* Parses a string into a Region object.
*
* @param {string} text
* @return {!shaka.extern.CueRegion}
* @private
*/
static parseRegion_(text) {
const VttTextParser = shaka.text.VttTextParser;
const parser = new shaka.util.TextParser(text);
// The region string looks like this:
// Region: id=fred width=50% lines=3 regionanchor=0%,100%
// viewportanchor=10%,90% scroll=up
const region = new shaka.text.CueRegion();
// Skip 'Region:'
parser.readWord();
parser.skipWhitespace();
let word = parser.readWord();
while (word) {
if (!VttTextParser.parseRegionSetting_(region, word)) {
shaka.log.warning(
'VTT parser encountered an invalid VTTRegion setting: ', word,
' The setting will be ignored.');
}
parser.skipWhitespace();
word = parser.readWord();
}
return region;
}
/**
* Parses a text block into a Cue object.
*
* @param {!Array.<string>} text
* @param {number} timeOffset
* @param {!Array.<!shaka.extern.CueRegion>} regions
* @return {shaka.text.Cue}
* @private
*/
static parseCue_(text, timeOffset, regions) {
const VttTextParser = shaka.text.VttTextParser;
// Skip empty blocks.
if (text.length == 1 && !text[0]) {
return null;
}
// Skip comment blocks.
if (/^NOTE($|[ \t])/.test(text[0])) {
return null;
}
// Skip style blocks.
if (text[0] == 'STYLE') {
return null;
}
let id = null;
if (!text[0].includes('-->')) {
id = text[0];
text.splice(0, 1);
}
// Parse the times.
const parser = new shaka.util.TextParser(text[0]);
let start = VttTextParser.parseTime_(parser);
const expect = parser.readRegex(/[ \t]+-->[ \t]+/g);
let end = VttTextParser.parseTime_(parser);
if (start == null || expect == null || end == null) {
throw new shaka.util.Error(
shaka.util.Error.Severity.CRITICAL,
shaka.util.Error.Category.TEXT,
shaka.util.Error.Code.INVALID_TEXT_CUE);
}
start += timeOffset;
end += timeOffset;
// Get the payload.
const payload = text.slice(1).join('\n').trim();
const cue = new shaka.text.Cue(start, end, payload);
// Parse optional settings.
parser.skipWhitespace();
let word = parser.readWord();
while (word) {
if (!VttTextParser.parseCueSetting(cue, word, regions)) {
shaka.log.warning('VTT parser encountered an invalid VTT setting: ',
word,
' The setting will be ignored.');
}
parser.skipWhitespace();
word = parser.readWord();
}
if (id != null) {
cue.id = id;
}
return cue;
}
/**
* Parses a WebVTT setting from the given word.
*
* @param {!shaka.text.Cue} cue
* @param {string} word
* @param {!Array.<!shaka.text.CueRegion>} regions
* @return {boolean} True on success.
*/
static parseCueSetting(cue, word, regions) {
const VttTextParser = shaka.text.VttTextParser;
let results = null;
if ((results = /^align:(start|middle|center|end|left|right)$/.exec(word))) {
VttTextParser.setTextAlign_(cue, results[1]);
} else if ((results = /^vertical:(lr|rl)$/.exec(word))) {
VttTextParser.setVerticalWritingMode_(cue, results[1]);
} else if ((results = /^size:([\d.]+)%$/.exec(word))) {
cue.size = Number(results[1]);
} else if ((results =
/^position:([\d.]+)%(?:,(line-left|line-right|center|start|end))?$/
.exec(word))) {
cue.position = Number(results[1]);
if (results[2]) {
VttTextParser.setPositionAlign_(cue, results[2]);
}
} else if ((results = /^region:(.*)$/.exec(word))) {
const region = VttTextParser.getRegionById_(regions, results[1]);
if (region) {
cue.region = region;
}
} else {
return VttTextParser.parsedLineValueAndInterpretation_(cue, word);
}
return true;
}
/**
*
* @param {!Array.<!shaka.text.CueRegion>} regions
* @param {string} id
* @return {?shaka.text.CueRegion}
* @private
*/
static getRegionById_(regions, id) {
const regionsWithId = regions.filter((region) => {
return region.id == id;
});
if (!regionsWithId.length) {
shaka.log.warning('VTT parser could not find a region with id: ',
id,
' The region will be ignored.');
return null;
}
goog.asserts.assert(regionsWithId.length == 1,
'VTTRegion ids should be unique!');
return regionsWithId[0];
}
/**
* Parses a WebVTTRegion setting from the given word.
*
* @param {!shaka.text.CueRegion} region
* @param {string} word
* @return {boolean} True on success.
* @private
*/
static parseRegionSetting_(region, word) {
let results = null;
if ((results = /^id=(.*)$/.exec(word))) {
region.id = results[1];
} else if ((results = /^width=(\d{1,2}|100)%$/.exec(word))) {
region.width = Number(results[1]);
} else if ((results = /^lines=(\d+)$/.exec(word))) {
region.height = Number(results[1]);
region.heightUnits = shaka.text.CueRegion.units.LINES;
} else if ((results = /^regionanchor=(\d{1,2}|100)%,(\d{1,2}|100)%$/
.exec(word))) {
region.regionAnchorX = Number(results[1]);
region.regionAnchorY = Number(results[2]);
} else if ((results = /^viewportanchor=(\d{1,2}|100)%,(\d{1,2}|100)%$/
.exec(word))) {
region.viewportAnchorX = Number(results[1]);
region.viewportAnchorY = Number(results[2]);
} else if ((results = /^scroll=up$/.exec(word))) {
region.scroll = shaka.text.CueRegion.scrollMode.UP;
} else {
return false;
}
return true;
}
/**
* @param {!shaka.text.Cue} cue
* @param {string} align
* @private
*/
static setTextAlign_(cue, align) {
const Cue = shaka.text.Cue;
if (align == 'middle') {
cue.textAlign = Cue.textAlign.CENTER;
} else {
goog.asserts.assert(align.toUpperCase() in Cue.textAlign,
align.toUpperCase() +
' Should be in Cue.textAlign values!');
cue.textAlign = Cue.textAlign[align.toUpperCase()];
}
}
/**
* @param {!shaka.text.Cue} cue
* @param {string} align
* @private
*/
static setPositionAlign_(cue, align) {
const Cue = shaka.text.Cue;
if (align == 'line-left' || align == 'start') {
cue.positionAlign = Cue.positionAlign.LEFT;
} else if (align == 'line-right' || align == 'end') {
cue.positionAlign = Cue.positionAlign.RIGHT;
} else {
cue.positionAlign = Cue.positionAlign.CENTER;
}
}
/**
* @param {!shaka.text.Cue} cue
* @param {string} value
* @private
*/
static setVerticalWritingMode_(cue, value) {
const Cue = shaka.text.Cue;
if (value == 'lr') {
cue.writingMode = Cue.writingMode.VERTICAL_LEFT_TO_RIGHT;
} else {
cue.writingMode = Cue.writingMode.VERTICAL_RIGHT_TO_LEFT;
}
}
/**
* @param {!shaka.text.Cue} cue
* @param {string} word
* @return {boolean}
* @private
*/
static parsedLineValueAndInterpretation_(cue, word) {
const Cue = shaka.text.Cue;
let results = null;
if ((results = /^line:([\d.]+)%(?:,(start|end|center))?$/.exec(word))) {
cue.lineInterpretation = Cue.lineInterpretation.PERCENTAGE;
cue.line = Number(results[1]);
if (results[2]) {
goog.asserts.assert(
results[2].toUpperCase() in Cue.lineAlign,
results[2].toUpperCase() + ' Should be in Cue.lineAlign values!');
cue.lineAlign = Cue.lineAlign[results[2].toUpperCase()];
}
} else if ((results =
/^line:(-?\d+)(?:,(start|end|center))?$/.exec(word))) {
cue.lineInterpretation = Cue.lineInterpretation.LINE_NUMBER;
cue.line = Number(results[1]);
if (results[2]) {
goog.asserts.assert(
results[2].toUpperCase() in Cue.lineAlign,
results[2].toUpperCase() + ' Should be in Cue.lineAlign values!');
cue.lineAlign = Cue.lineAlign[results[2].toUpperCase()];
}
} else {
return false;
}
return true;
}
/**
* Parses a WebVTT time from the given parser.
*
* @param {!shaka.util.TextParser} parser
* @return {?number}
* @private
*/
static parseTime_(parser) {
// 00:00.000 or 00:00:00.000 or 0:00:00.000 or
// 00:00.00 or 00:00:00.00 or 0:00:00.00
const regexExpresion = /(?:(\d{1,}):)?(\d{2}):(\d{2})\.(\d{2,3})/g;
const results = parser.readRegex(regexExpresion);
if (results == null) {
return null;
}
// This capture is optional, but will still be in the array as undefined,
// in which case it is 0.
const hours = Number(results[1]) || 0;
const minutes = Number(results[2]);
const seconds = Number(results[3]);
const milliseconds = Number(results[4]);
if (minutes > 59 || seconds > 59) {
return null;
}
return (milliseconds / 1000) + seconds + (minutes * 60) + (hours * 3600);
}
};
/**
* @const {number}
* @private
*/
shaka.text.VttTextParser.MPEG_TIMESCALE_ = 90000;
/**
* At this value, timestamps roll over in TS content.
* @const {number}
* @private
*/
shaka.text.VttTextParser.TS_ROLLOVER_ = 0x200000000;
shaka.text.TextEngine.registerParser(
'text/vtt', () => new shaka.text.VttTextParser());
shaka.text.TextEngine.registerParser(
'text/vtt; codecs="vtt"', () => new shaka.text.VttTextParser());
shaka.text.TextEngine.registerParser(
'text/vtt; codecs="wvtt"', () => new shaka.text.VttTextParser());