Zazama / node-id3

/**

 * ID3 header size uses only 7 bits of a byte, bit shift is needed.

 * @returns Return a Buffer of 4 bytes with the encoded size

 */

export function encodeSize(size: number) {

    const byte_3 = size & 0x7F

    const byte_2 = (size >> 7) & 0x7F

    const byte_1 = (size >> 14) & 0x7F

    const byte_0 = (size >> 21) & 0x7F

    return Buffer.from([byte_0, byte_1, byte_2, byte_3])

}

/**

 * Decode the encoded size from an ID3 header.

 */

export function decodeSize(encodedSize: Buffer) {

    return (

        (encodedSize[0] << 21) +

        (encodedSize[1] << 14) +

        (encodedSize[2] << 7) +

        encodedSize[3]

    )

}

export function getFrameSize(buffer: Buffer, decode: boolean, version: number) {

    const decodeBytes = version > 2 ?

        [buffer[4], buffer[5], buffer[6], buffer[7]] :

        [buffer[3], buffer[4], buffer[5]]

    if (decode) {

        return decodeSize(Buffer.from(decodeBytes))

    }

    return Buffer.from(decodeBytes).readUIntBE(0, decodeBytes.length)

}