wavefile
Version:
Create, read and write wav files according to the specs.
148 lines (141 loc) • 4.52 kB
JavaScript
/*
* alawmulaw: A-Law and mu-Law codecs in JavaScript.
* https://github.com/rochars/alawmulaw
*
* Copyright (c) 2018-2019 Rafael da Silva Rocha.
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
*/
/**
* @fileoverview mu-Law codec.
* @see https://github.com/rochars/wavefile
* @see https://github.com/rochars/alawmulaw
*/
/**
* @type {number}
* @private
*/
const BIAS = 0x84;
/**
* @type {number}
* @private
*/
const CLIP = 32635;
/**
* @type {Array<number>}
* @private
*/
const encodeTable = [
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];
/**
* @type {Array<number>}
* @private
*/
const decodeTable = [0,132,396,924,1980,4092,8316,16764];
/**
* Encode a 16-bit linear PCM sample as 8-bit mu-Law.
* @param {number} sample A 16-bit PCM sample
* @return {number}
*/
export function encodeSample(sample) {
/** @type {number} */
let sign;
/** @type {number} */
let exponent;
/** @type {number} */
let mantissa;
/** @type {number} */
let muLawSample;
/** get the sample into sign-magnitude **/
sign = (sample >> 8) & 0x80;
if (sign != 0) sample = -sample;
/** convert from 16 bit linear to ulaw **/
sample = sample + BIAS;
if (sample > CLIP) sample = CLIP;
exponent = encodeTable[(sample>>7) & 0xFF];
mantissa = (sample >> (exponent+3)) & 0x0F;
muLawSample = ~(sign | (exponent << 4) | mantissa);
/** return the result **/
return muLawSample;
}
/**
* Decode a 8-bit mu-Law sample as 16-bit PCM.
* @param {number} muLawSample The 8-bit mu-Law sample
* @return {number}
*/
export function decodeSample(muLawSample) {
/** @type {number} */
let sign;
/** @type {number} */
let exponent;
/** @type {number} */
let mantissa;
/** @type {number} */
let sample;
muLawSample = ~muLawSample;
sign = (muLawSample & 0x80);
exponent = (muLawSample >> 4) & 0x07;
mantissa = muLawSample & 0x0F;
sample = decodeTable[exponent] + (mantissa << (exponent+3));
if (sign != 0) sample = -sample;
return sample;
}
/**
* Encode 16-bit linear PCM samples into 8-bit mu-Law samples.
* @param {!Int16Array} samples A array of 16-bit PCM samples.
* @return {!Uint8Array}
*/
export function encode(samples) {
/** @type {!Uint8Array} */
let muLawSamples = new Uint8Array(samples.length);
for (let i = 0, len = samples.length; i < len; i++) {
muLawSamples[i] = encodeSample(samples[i]);
}
return muLawSamples;
}
/**
* Decode 8-bit mu-Law samples into 16-bit PCM samples.
* @param {!Uint8Array} samples A array of 8-bit mu-Law samples.
* @return {!Int16Array}
*/
export function decode(samples) {
/** @type {!Int16Array} */
let pcmSamples = new Int16Array(samples.length);
for (let i = 0, len = samples.length; i < len; i++) {
pcmSamples[i] = decodeSample(samples[i]);
}
return pcmSamples;
}