prx-wavefile
Version:
Create, read and write wav files according to the specs.
126 lines (119 loc) • 3.94 kB
JavaScript
/*
* alawmulaw: A-Law and mu-Law codecs in JavaScript.
* https://github.com/rochars/alawmulaw
*
* Copyright (c) 2018 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 A-Law codec.
* @see https://github.com/rochars/wavefile
* @see https://github.com/rochars/alawmulaw
*/
/** @type {!Array<number>} */
const LOG_TABLE = [
1,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
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,
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
];
/**
* Encode a 16-bit linear PCM sample as 8-bit A-Law.
* @param {number} sample A 16-bit PCM sample
* @return {number}
*/
export function encodeSample(sample) {
/** @type {number} */
let compandedValue;
sample = (sample ==-32768) ? -32767 : sample;
/** @type {number} */
let sign = ((~sample) >> 8) & 0x80;
if (!sign) {
sample = sample * -1;
}
if (sample > 32635) {
sample = 32635;
}
if (sample >= 256) {
/** @type {number} */
let exponent = LOG_TABLE[(sample >> 8) & 0x7F];
/** @type {number} */
let mantissa = (sample >> (exponent + 3) ) & 0x0F;
compandedValue = ((exponent << 4) | mantissa);
} else {
compandedValue = sample >> 4;
}
return compandedValue ^ (sign ^ 0x55);
}
/**
* Decode a 8-bit A-Law sample as 16-bit PCM.
* @param {number} aLawSample The 8-bit A-Law sample
* @return {number}
*/
export function decodeSample(aLawSample) {
/** @type {number} */
let sign = 0;
aLawSample ^= 0x55;
if ((aLawSample & 0x80) !== 0) {
aLawSample &= ~(1 << 7);
sign = -1;
}
/** @type {number} */
let position = ((aLawSample & 0xF0) >> 4) + 4;
/** @type {number} */
let decoded = 0;
if (position != 4) {
decoded = ((1 << position) |
((aLawSample & 0x0F) << (position - 4)) |
(1 << (position - 5)));
} else {
decoded = (aLawSample << 1)|1;
}
decoded = (sign === 0) ? (decoded) : (-decoded);
return (decoded * 8) * -1;
}
/**
* Encode 16-bit linear PCM samples as 8-bit A-Law samples.
* @param {!Int16Array} samples A array of 16-bit PCM samples.
* @return {!Uint8Array}
*/
export function encode(samples) {
/** @type {!Uint8Array} */
let aLawSamples = new Uint8Array(samples.length);
for (let i = 0, len = samples.length; i < len; i++) {
aLawSamples[i] = encodeSample(samples[i]);
}
return aLawSamples;
}
/**
* Decode 8-bit A-Law samples into 16-bit linear PCM samples.
* @param {!Uint8Array} samples A array of 8-bit A-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;
}