music-metadata
Version:
Music metadata parser for Node.js, supporting virtual any audio and tag format.
117 lines (116 loc) • 4.44 kB
JavaScript
import * as Token from 'token-types';
import { FourCcToken } from '../common/FourCC.js';
export const DataType = {
text_utf8: 0,
binary: 1,
external_info: 2,
reserved: 3
};
/**
* APE_DESCRIPTOR: defines the sizes (and offsets) of all the pieces, as well as the MD5 checksum
*/
export const DescriptorParser = {
len: 52,
get: (buf, off) => {
return {
// should equal 'MAC '
ID: FourCcToken.get(buf, off),
// versionIndex number * 1000 (3.81 = 3810) (remember that 4-byte alignment causes this to take 4-bytes)
version: Token.UINT32_LE.get(buf, off + 4) / 1000,
// the number of descriptor bytes (allows later expansion of this header)
descriptorBytes: Token.UINT32_LE.get(buf, off + 8),
// the number of header APE_HEADER bytes
headerBytes: Token.UINT32_LE.get(buf, off + 12),
// the number of header APE_HEADER bytes
seekTableBytes: Token.UINT32_LE.get(buf, off + 16),
// the number of header data bytes (from original file)
headerDataBytes: Token.UINT32_LE.get(buf, off + 20),
// the number of bytes of APE frame data
apeFrameDataBytes: Token.UINT32_LE.get(buf, off + 24),
// the high order number of APE frame data bytes
apeFrameDataBytesHigh: Token.UINT32_LE.get(buf, off + 28),
// the terminating data of the file (not including tag data)
terminatingDataBytes: Token.UINT32_LE.get(buf, off + 32),
// the MD5 hash of the file (see notes for usage... it's a little tricky)
fileMD5: new Token.Uint8ArrayType(16).get(buf, off + 36)
};
}
};
/**
* APE_HEADER: describes all of the necessary information about the APE file
*/
export const Header = {
len: 24,
get: (buf, off) => {
return {
// the compression level (see defines I.E. COMPRESSION_LEVEL_FAST)
compressionLevel: Token.UINT16_LE.get(buf, off),
// any format flags (for future use)
formatFlags: Token.UINT16_LE.get(buf, off + 2),
// the number of audio blocks in one frame
blocksPerFrame: Token.UINT32_LE.get(buf, off + 4),
// the number of audio blocks in the final frame
finalFrameBlocks: Token.UINT32_LE.get(buf, off + 8),
// the total number of frames
totalFrames: Token.UINT32_LE.get(buf, off + 12),
// the bits per sample (typically 16)
bitsPerSample: Token.UINT16_LE.get(buf, off + 16),
// the number of channels (1 or 2)
channel: Token.UINT16_LE.get(buf, off + 18),
// the sample rate (typically 44100)
sampleRate: Token.UINT32_LE.get(buf, off + 20)
};
}
};
/**
* APE Tag Header/Footer Version 2.0
* TAG: describes all the properties of the file [optional]
*/
export const TagFooter = {
len: 32,
get: (buf, off) => {
return {
// should equal 'APETAGEX'
ID: new Token.StringType(8, 'ascii').get(buf, off),
// equals CURRENT_APE_TAG_VERSION
version: Token.UINT32_LE.get(buf, off + 8),
// the complete size of the tag, including this footer (excludes header)
size: Token.UINT32_LE.get(buf, off + 12),
// the number of fields in the tag
fields: Token.UINT32_LE.get(buf, off + 16),
// reserved for later use (must be zero),
flags: parseTagFlags(Token.UINT32_LE.get(buf, off + 20))
};
}
};
/**
* APE Tag v2.0 Item Header
*/
export const TagItemHeader = {
len: 8,
get: (buf, off) => {
return {
// Length of assigned value in bytes
size: Token.UINT32_LE.get(buf, off),
// reserved for later use (must be zero),
flags: parseTagFlags(Token.UINT32_LE.get(buf, off + 4))
};
}
};
export function parseTagFlags(flags) {
return {
containsHeader: isBitSet(flags, 31),
containsFooter: isBitSet(flags, 30),
isHeader: isBitSet(flags, 29),
readOnly: isBitSet(flags, 0),
dataType: (flags & 6) >> 1
};
}
/**
* @param num {number}
* @param bit 0 is least significant bit (LSB)
* @return {boolean} true if bit is 1; otherwise false
*/
export function isBitSet(num, bit) {
return (num & 1 << bit) !== 0;
}