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import { VTTParser } from './vttparser';
import { utf8ArrayToStr } from '../demux/id3';
import {
RationalTimestamp,
toMpegTsClockFromTimescale,
} from './timescale-conversion';
import { normalizePts } from '../remux/mp4-remuxer';
import type { VTTCCs } from '../types/vtt';
const LINEBREAKS = /\r\n|\n\r|\n|\r/g;
// String.prototype.startsWith is not supported in IE11
const startsWith = function (
inputString: string,
searchString: string,
position: number = 0
) {
return (
inputString.slice(position, position + searchString.length) === searchString
);
};
const cueString2millis = function (timeString: string) {
let ts = parseInt(timeString.slice(-3));
const secs = parseInt(timeString.slice(-6, -4));
const mins = parseInt(timeString.slice(-9, -7));
const hours =
timeString.length > 9
? parseInt(timeString.substring(0, timeString.indexOf(':')))
: 0;
if (
!Number.isFinite(ts) ||
!Number.isFinite(secs) ||
!Number.isFinite(mins) ||
!Number.isFinite(hours)
) {
throw Error(`Malformed X-TIMESTAMP-MAP: Local:${timeString}`);
}
ts += 1000 * secs;
ts += 60 * 1000 * mins;
ts += 60 * 60 * 1000 * hours;
return ts;
};
// From https://github.com/darkskyapp/string-hash
const hash = function (text: string) {
let hash = 5381;
let i = text.length;
while (i) {
hash = (hash * 33) ^ text.charCodeAt(--i);
}
return (hash >>> 0).toString();
};
// Create a unique hash id for a cue based on start/end times and text.
// This helps timeline-controller to avoid showing repeated captions.
export function generateCueId(
startTime: number,
endTime: number,
text: string
) {
return hash(startTime.toString()) + hash(endTime.toString()) + hash(text);
}
const calculateOffset = function (vttCCs: VTTCCs, cc, presentationTime) {
let currCC = vttCCs[cc];
let prevCC = vttCCs[currCC.prevCC];
// This is the first discontinuity or cues have been processed since the last discontinuity
// Offset = current discontinuity time
if (!prevCC || (!prevCC.new && currCC.new)) {
vttCCs.ccOffset = vttCCs.presentationOffset = currCC.start;
currCC.new = false;
return;
}
// There have been discontinuities since cues were last parsed.
// Offset = time elapsed
while (prevCC?.new) {
vttCCs.ccOffset += currCC.start - prevCC.start;
currCC.new = false;
currCC = prevCC;
prevCC = vttCCs[currCC.prevCC];
}
vttCCs.presentationOffset = presentationTime;
};
export function parseWebVTT(
vttByteArray: ArrayBuffer,
initPTS: RationalTimestamp | undefined,
vttCCs: VTTCCs,
cc: number,
timeOffset: number,
callBack: (cues: VTTCue[]) => void,
errorCallBack: (error: Error) => void
) {
const parser = new VTTParser();
// Convert byteArray into string, replacing any somewhat exotic linefeeds with "\n", then split on that character.
// Uint8Array.prototype.reduce is not implemented in IE11
const vttLines = utf8ArrayToStr(new Uint8Array(vttByteArray))
.trim()
.replace(LINEBREAKS, '\n')
.split('\n');
const cues: VTTCue[] = [];
const init90kHz = initPTS
? toMpegTsClockFromTimescale(initPTS.baseTime, initPTS.timescale)
: 0;
let cueTime = '00:00.000';
let timestampMapMPEGTS = 0;
let timestampMapLOCAL = 0;
let parsingError: Error;
let inHeader = true;
parser.oncue = function (cue: VTTCue) {
// Adjust cue timing; clamp cues to start no earlier than - and drop cues that don't end after - 0 on timeline.
const currCC = vttCCs[cc];
let cueOffset = vttCCs.ccOffset;
// Calculate subtitle PTS offset
const webVttMpegTsMapOffset = (timestampMapMPEGTS - init90kHz) / 90000;
// Update offsets for new discontinuities
if (currCC?.new) {
if (timestampMapLOCAL !== undefined) {
// When local time is provided, offset = discontinuity start time - local time
cueOffset = vttCCs.ccOffset = currCC.start;
} else {
calculateOffset(vttCCs, cc, webVttMpegTsMapOffset);
}
}
if (webVttMpegTsMapOffset) {
if (!initPTS) {
parsingError = new Error('Missing initPTS for VTT MPEGTS');
return;
}
// If we have MPEGTS, offset = presentation time + discontinuity offset
cueOffset = webVttMpegTsMapOffset - vttCCs.presentationOffset;
}
const duration = cue.endTime - cue.startTime;
const startTime =
normalizePts(
(cue.startTime + cueOffset - timestampMapLOCAL) * 90000,
timeOffset * 90000
) / 90000;
cue.startTime = Math.max(startTime, 0);
cue.endTime = Math.max(startTime + duration, 0);
//trim trailing webvtt block whitespaces
const text = cue.text.trim();
// Fix encoding of special characters
cue.text = decodeURIComponent(encodeURIComponent(text));
// If the cue was not assigned an id from the VTT file (line above the content), create one.
if (!cue.id) {
cue.id = generateCueId(cue.startTime, cue.endTime, text);
}
if (cue.endTime > 0) {
cues.push(cue);
}
};
parser.onparsingerror = function (error: Error) {
parsingError = error;
};
parser.onflush = function () {
if (parsingError) {
errorCallBack(parsingError);
return;
}
callBack(cues);
};
// Go through contents line by line.
vttLines.forEach((line) => {
if (inHeader) {
// Look for X-TIMESTAMP-MAP in header.
if (startsWith(line, 'X-TIMESTAMP-MAP=')) {
// Once found, no more are allowed anyway, so stop searching.
inHeader = false;
// Extract LOCAL and MPEGTS.
line
.slice(16)
.split(',')
.forEach((timestamp) => {
if (startsWith(timestamp, 'LOCAL:')) {
cueTime = timestamp.slice(6);
} else if (startsWith(timestamp, 'MPEGTS:')) {
timestampMapMPEGTS = parseInt(timestamp.slice(7));
}
});
try {
// Convert cue time to seconds
timestampMapLOCAL = cueString2millis(cueTime) / 1000;
} catch (error) {
parsingError = error;
}
// Return without parsing X-TIMESTAMP-MAP line.
return;
} else if (line === '') {
inHeader = false;
}
}
// Parse line by default.
parser.parse(line + '\n');
});
parser.flush();
}