66 lines
3.0 KiB
JavaScript
66 lines
3.0 KiB
JavaScript
import initDebug from 'debug';
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import * as AtomToken from './AtomToken.js';
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import { Header } from './AtomToken.js';
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const debug = initDebug('music-metadata:parser:MP4:Atom');
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export class Atom {
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static async readAtom(tokenizer, dataHandler, parent, remaining) {
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// Parse atom header
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const offset = tokenizer.position;
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debug(`Reading next token on offset=${offset}...`); // buf.toString('ascii')
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const header = await tokenizer.readToken(AtomToken.Header);
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const extended = header.length === 1n;
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if (extended) {
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header.length = await tokenizer.readToken(AtomToken.ExtendedSize);
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}
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const atomBean = new Atom(header, extended, parent);
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const payloadLength = atomBean.getPayloadLength(remaining);
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debug(`parse atom name=${atomBean.atomPath}, extended=${atomBean.extended}, offset=${offset}, len=${atomBean.header.length}`); // buf.toString('ascii')
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await atomBean.readData(tokenizer, dataHandler, payloadLength);
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return atomBean;
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}
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constructor(header, extended, parent) {
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this.header = header;
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this.extended = extended;
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this.parent = parent;
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this.children = [];
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this.atomPath = (this.parent ? `${this.parent.atomPath}.` : '') + this.header.name;
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}
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getHeaderLength() {
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return this.extended ? 16 : 8;
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}
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getPayloadLength(remaining) {
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return (this.header.length === 0n ? remaining : Number(this.header.length)) - this.getHeaderLength();
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}
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async readAtoms(tokenizer, dataHandler, size) {
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while (size > 0) {
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const atomBean = await Atom.readAtom(tokenizer, dataHandler, this, size);
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this.children.push(atomBean);
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size -= atomBean.header.length === 0n ? size : Number(atomBean.header.length);
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}
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}
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async readData(tokenizer, dataHandler, remaining) {
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switch (this.header.name) {
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// "Container" atoms, contains nested atoms
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case 'moov': // The Movie Atom: contains other atoms
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case 'udta': // User defined atom
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case 'mdia': // Media atom
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case 'minf': // Media Information Atom
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case 'stbl': // The Sample Table Atom
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case '<id>':
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case 'ilst':
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case 'tref':
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case 'moof':
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return this.readAtoms(tokenizer, dataHandler, this.getPayloadLength(remaining));
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case 'meta': { // Metadata Atom, ref: https://developer.apple.com/library/content/documentation/QuickTime/QTFF/Metadata/Metadata.html#//apple_ref/doc/uid/TP40000939-CH1-SW8
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// meta has 4 bytes of padding, ignore
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const peekHeader = await tokenizer.peekToken(Header);
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const paddingLength = peekHeader.name === 'hdlr' ? 0 : 4;
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await tokenizer.ignore(paddingLength);
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return this.readAtoms(tokenizer, dataHandler, this.getPayloadLength(remaining) - paddingLength);
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}
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default:
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return dataHandler(this, remaining);
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}
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}
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}
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