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const { Transform } = require('stream');
const OGG_PAGE_HEADER_SIZE = 26;
const STREAM_STRUCTURE_VERSION = 0;
const OGGS_HEADER = Buffer.from('OggS'.split('').map(x => x.charCodeAt(0)));
const OPUS_HEAD = Buffer.from('OpusHead'.split('').map(x => x.charCodeAt(0)));
const OPUS_TAGS = Buffer.from('OpusTags'.split('').map(x => x.charCodeAt(0)));
class OggOpusTransform extends Transform {
constructor() {
super();
this._remainder = null;
this._head = null;
}
_transform(chunk, encoding, done) {
if (this._remainder) {
chunk = Buffer.concat([this._remainder, chunk]);
this._remainder = null;
}
while (chunk) {
try {
const result = this.readPage(chunk);
if (result) chunk = result;
else break;
} catch (err) {
this.emit('error', err);
}
}
this._remainder = chunk;
done();
}
/**
* Reads a page from a buffer
* @param {Buffer} chunk The chunk containing the page
* @returns {boolean|Buffer}
*/
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}`);
}
const pageSegments = chunk.readUInt8(26),
table = chunk.slice(27, 27 + pageSegments);
let sizes = [], totalSize = 0;
for (let i = 0; i < pageSegments;) {
let size = 0, x = 255;
while (x === 255) {
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('opusTags', segment);
else this.push(segment);
} else if (header.equals(OPUS_HEAD)) {
this._head = segment;
} else {
throw Error(`Invalid segment ${segment}`);
}
start += size;
}
return chunk.slice(start);
}
}
module.exports = OggOpusTransform;
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