music-metadata/lib/flac/FlacToken.js

Music metadata parser for Node.js, supporting virtual any audio and tag format.

import * as util from '../common/Util.js';
import { UINT16_BE, UINT24_BE, Uint8ArrayType } from 'token-types';
/**
 * FLAC supports up to 128 kinds of metadata blocks; currently the following are defined:
 * ref: https://xiph.org/flac/format.html#metadata_block
 */
export const BlockType = {
    STREAMINFO: 0, // STREAMINFO
    PADDING: 1, // PADDING
    APPLICATION: 2, // APPLICATION
    SEEKTABLE: 3, // SEEKTABLE
    VORBIS_COMMENT: 4, // VORBIS_COMMENT
    CUESHEET: 5, // CUESHEET
    PICTURE: 6 // PICTURE
};
export const BlockHeader = {
    len: 4,
    get: (buf, off) => {
        return {
            lastBlock: util.getBit(buf, off, 7),
            type: util.getBitAllignedNumber(buf, off, 1, 7),
            length: UINT24_BE.get(buf, off + 1)
        };
    }
};
/**
 * METADATA_BLOCK_DATA
 * Ref: https://xiph.org/flac/format.html#metadata_block_streaminfo
 */
export const BlockStreamInfo = {
    len: 34,
    get: (buf, off) => {
        return {
            // The minimum block size (in samples) used in the stream.
            minimumBlockSize: UINT16_BE.get(buf, off),
            // The maximum block size (in samples) used in the stream.
            // (Minimum blocksize == maximum blocksize) implies a fixed-blocksize stream.
            maximumBlockSize: UINT16_BE.get(buf, off + 2) / 1000,
            // The minimum frame size (in bytes) used in the stream.
            // May be 0 to imply the value is not known.
            minimumFrameSize: UINT24_BE.get(buf, off + 4),
            // The maximum frame size (in bytes) used in the stream.
            // May be 0 to imply the value is not known.
            maximumFrameSize: UINT24_BE.get(buf, off + 7),
            // Sample rate in Hz. Though 20 bits are available,
            // the maximum sample rate is limited by the structure of frame headers to 655350Hz.
            // Also, a value of 0 is invalid.
            sampleRate: UINT24_BE.get(buf, off + 10) >> 4,
            // probably slower: sampleRate: common.getBitAllignedNumber(buf, off + 10, 0, 20),
            // (number of channels)-1. FLAC supports from 1 to 8 channels
            channels: util.getBitAllignedNumber(buf, off + 12, 4, 3) + 1,
            // bits per sample)-1.
            // FLAC supports from 4 to 32 bits per sample. Currently the reference encoder and decoders only support up to 24 bits per sample.
            bitsPerSample: util.getBitAllignedNumber(buf, off + 12, 7, 5) + 1,
            // Total samples in stream.
            // 'Samples' means inter-channel sample, i.e. one second of 44.1Khz audio will have 44100 samples regardless of the number of channels.
            // A value of zero here means the number of total samples is unknown.
            totalSamples: util.getBitAllignedNumber(buf, off + 13, 4, 36),
            // the MD5 hash of the file (see notes for usage... it's a littly tricky)
            fileMD5: new Uint8ArrayType(16).get(buf, off + 18)
        };
    }
};