music-metadata
Version:
Music metadata parser for Node.js, supporting virtual any audio and tag format.
94 lines (93 loc) • 3.58 kB
JavaScript
// lib/id3v2/FrameHeader.ts
import * as Token from 'token-types';
import * as util from '../common/Util.js';
import { UINT32SYNCSAFE } from './ID3v2Token.js';
import { textDecode } from '@borewit/text-codec';
import { Id3v2ContentError } from './FrameParser.js';
/**
* Frame header length (bytes) depending on ID3v2 major version.
*/
export function getFrameHeaderLength(majorVer) {
switch (majorVer) {
case 2: return 6;
case 3:
case 4: return 10;
default: throw makeUnexpectedMajorVersionError(majorVer);
}
}
function readFrameFlags(b, majorVer) {
// ID3v2.3 and ID3v2.4 use different bit layouts for the frame status and format flags.
if (majorVer === 3) {
// ID3v2.3: status `%abc00000`, format `%ijk00000` (https://id3.org/id3v2.3.0)
return {
status: {
tag_alter_preservation: util.getBit(b, 0, 7),
file_alter_preservation: util.getBit(b, 0, 6),
read_only: util.getBit(b, 0, 5)
},
format: {
compression: util.getBit(b, 1, 7),
encryption: util.getBit(b, 1, 6),
grouping_identity: util.getBit(b, 1, 5),
// Unsynchronisation and data-length-indicator do not exist as per-frame flags in ID3v2.3.
unsynchronisation: false,
data_length_indicator: false
}
};
}
// ID3v2.4: status `%0abc0000`, format `%0h00kmnp` (https://id3.org/id3v2.4.0-structure)
return {
status: {
tag_alter_preservation: util.getBit(b, 0, 6),
file_alter_preservation: util.getBit(b, 0, 5),
read_only: util.getBit(b, 0, 4)
},
format: {
grouping_identity: util.getBit(b, 1, 6),
compression: util.getBit(b, 1, 3),
encryption: util.getBit(b, 1, 2),
unsynchronisation: util.getBit(b, 1, 1),
data_length_indicator: util.getBit(b, 1, 0)
}
};
}
/**
* Factory: parse a frame header from its header bytes (6 for v2.2, 10 for v2.3/v2.4).
*
* Note: It only *parses* and does light validation. It does not read payload bytes.
*/
export function readFrameHeader(uint8Array, majorVer, warningCollector) {
switch (majorVer) {
case 2:
return parseFrameHeaderV22(uint8Array, majorVer, warningCollector);
case 3:
case 4:
return parseFrameHeaderV23V24(uint8Array, majorVer, warningCollector);
default:
throw makeUnexpectedMajorVersionError(majorVer);
}
}
function parseFrameHeaderV22(uint8Array, majorVer, warningCollector) {
const header = {
id: textDecode(uint8Array.subarray(0, 3), 'ascii'),
length: Token.UINT24_BE.get(uint8Array, 3)
};
if (!header.id.match(/^[A-Z0-9]{3}$/)) {
warningCollector.addWarning(`Invalid ID3v2.${majorVer} frame-header-ID: ${header.id}`);
}
return header;
}
function parseFrameHeaderV23V24(uint8Array, majorVer, warningCollector) {
const header = {
id: textDecode(uint8Array.subarray(0, 4), 'ascii'),
length: (majorVer === 4 ? UINT32SYNCSAFE : Token.UINT32_BE).get(uint8Array, 4),
flags: readFrameFlags(uint8Array.subarray(8, 10), majorVer)
};
if (!header.id.match(/^[A-Z0-9]{4}$/)) {
warningCollector.addWarning(`Invalid ID3v2.${majorVer} frame-header-ID: ${header.id}`);
}
return header;
}
function makeUnexpectedMajorVersionError(majorVer) {
throw new Id3v2ContentError(`Unexpected majorVer: ${majorVer}`);
}