@echogarden/wave-codec/dist/codecs/Mulaw.js

A fully-featured WAVE format encoder and decoder. Written in pure TypeScript.

/////////////////////////////////////////////////////////////////////////////////////////////
// Encode 16-bit linear PCM samples into 8-bit mu-Law samples.
/////////////////////////////////////////////////////////////////////////////////////////////
export function encodeMulaw(pcmSamples) {
    const muLawSamples = new Uint8Array(pcmSamples.length);
    for (let i = 0; i < pcmSamples.length; i++) {
        muLawSamples[i] = pcmToMulawSample(pcmSamples[i]);
    }
    return muLawSamples;
}
/////////////////////////////////////////////////////////////////////////////////////////////
// Decode 8-bit mu-Law samples into 16-bit PCM samples.
/////////////////////////////////////////////////////////////////////////////////////////////
export function decodeMulaw(muLawSamples) {
    const pcmSamples = new Int16Array(muLawSamples.length);
    for (let i = 0; i < muLawSamples.length; i++) {
        pcmSamples[i] = mulawToPcmSample(muLawSamples[i]);
    }
    return pcmSamples;
}
/////////////////////////////////////////////////////////////////////////////////////////////
// Encode a 16-bit linear PCM sample as 8-bit mu-Law
/////////////////////////////////////////////////////////////////////////////////////////////
export function pcmToMulawSample(pcmSample) {
    // Get the sample into sign-magnitude
    // Get sign bit
    const sign = (pcmSample >> 8) & 0x80;
    if (sign !== 0) {
        pcmSample = -pcmSample;
    }
    // Convert from 16 bit linear to ulaw
    pcmSample += 132; // 0x84
    if (pcmSample > 32635) {
        pcmSample = 32635;
    }
    const exponent = encodingLookup[(pcmSample >> 7) & 0xff];
    const mantissa = (pcmSample >> (exponent + 3)) & 0x0f;
    const mulawSample = ~(sign | (exponent << 4) | mantissa);
    return mulawSample;
}
/////////////////////////////////////////////////////////////////////////////////////////////
// Decode a 8-bit mu-Law sample as 16-bit PCM.
/////////////////////////////////////////////////////////////////////////////////////////////
export function mulawToPcmSample(muLawSample) {
    muLawSample = ~muLawSample;
    const sign = muLawSample & 0x80;
    const exponent = (muLawSample >> 4) & 0x07;
    const mantissa = muLawSample & 0x0f;
    let pcmSample = decodingLookup[exponent] + (mantissa << (exponent + 3));
    if (sign !== 0) {
        pcmSample = -pcmSample;
    }
    return pcmSample;
}
/////////////////////////////////////////////////////////////////////////////////////////////
// Encoding lookup table
/////////////////////////////////////////////////////////////////////////////////////////////
const encodingLookup = new Uint8Array([
    0, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
    4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4, 4,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
    7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7
]);
const decodingLookup = new Uint16Array([0, 132, 396, 924, 1980, 4092, 8316, 16764]);
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