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const { Transform } = require('stream');
const OGG_PAGE_HEADER_SIZE = 26;
const STREAM_STRUCTURE_VERSION = 0;
const charCode = x => x.charCodeAt(0);
const OGGS_HEADER = Buffer.from([...'OggS'].map(charCode));
const OPUS_HEAD = Buffer.from([...'OpusHead'].map(charCode));
const OPUS_TAGS = Buffer.from([...'OpusTags'].map(charCode));
/**
* Demuxes an Ogg stream (containing Opus audio) to output an Opus stream.
* @extends {TransformStream}
* @memberof opus
*/
class OggDemuxer extends Transform {
/**
* Creates a new OggOpus demuxer.
* @param {Object} [options] options that you would pass to a regular Transform stream.
* @memberof opus
*/
constructor(options = {}) {
super(Object.assign({ readableObjectMode: true }, options));
this._remainder = null;
this._head = null;
this._bitstream = null;
}
_transform(chunk, encoding, done) {
if (this._remainder) {
chunk = Buffer.concat([this._remainder, chunk]);
this._remainder = null;
}
while (chunk) {
const result = this._readPage(chunk);
if (result) chunk = result;
else break;
}
this._remainder = chunk;
done();
}
/**
* Reads a page from a buffer
* @private
* @param {Buffer} chunk the chunk containing the page
* @returns {boolean|Buffer} if a buffer, it will be a slice of the excess data of the original, otherwise it will be
* false and would indicate that there is not enough data to go ahead with reading this page.
*/
_readPage(chunk) {
if (chunk.length < OGG_PAGE_HEADER_SIZE) {
return false;
}
if (!chunk.slice(0, 4).equals(OGGS_HEADER)) {
throw Error(`capture_pattern is not ${OGGS_HEADER}`);
}
if (chunk.readUInt8(4) !== STREAM_STRUCTURE_VERSION) {
throw Error(`stream_structure_version is not ${STREAM_STRUCTURE_VERSION}`);
}
if (chunk.length < 27) return false;
const pageSegments = chunk.readUInt8(26);
if (chunk.length < 27 + pageSegments) return false;
const table = chunk.slice(27, 27 + pageSegments);
const bitstream = chunk.readUInt32BE(14);
let sizes = [], totalSize = 0;
for (let i = 0; i < pageSegments;) {
let size = 0, x = 255;
while (x === 255) {
if (i >= table.length) return false;
x = table.readUInt8(i);
i++;
size += x;
}
sizes.push(size);
totalSize += size;
}
if (chunk.length < 27 + pageSegments + totalSize) return false;
let start = 27 + pageSegments;
for (const size of sizes) {
const segment = chunk.slice(start, start + size);
const header = segment.slice(0, 8);
if (this._head) {
if (header.equals(OPUS_TAGS)) this.emit('tags', segment);
else if (this._bitstream === bitstream) this.push(segment);
} else if (header.equals(OPUS_HEAD)) {
this.emit('head', segment);
this._head = segment;
this._bitstream = bitstream;
} else {
this.emit('unknownSegment', segment);
}
start += size;
}
return chunk.slice(start);
}
}
/**
* Emitted when the demuxer encounters the opus head.
* @event OggDemuxer#head
* @memberof opus
* @param {Buffer} segment a buffer containing the opus head data.
*/
/**
* Emitted when the demuxer encounters opus tags.
* @event OggDemuxer#tags
* @memberof opus
* @param {Buffer} segment a buffer containing the opus tags.
*/
module.exports = OggDemuxer;
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