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/* |
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* alawmulaw: A-Law and mu-Law codecs in JavaScript. |
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* https://github.com/rochars/alawmulaw |
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* |
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* Copyright (c) 2018 Rafael da Silva Rocha. |
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* |
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* Permission is hereby granted, free of charge, to any person obtaining |
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* a copy of this software and associated documentation files (the |
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* "Software"), to deal in the Software without restriction, including |
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* without limitation the rights to use, copy, modify, merge, publish, |
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* distribute, sublicense, and/or sell copies of the Software, and to |
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* permit persons to whom the Software is furnished to do so, subject to |
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* the following conditions: |
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* |
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* The above copyright notice and this permission notice shall be |
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* included in all copies or substantial portions of the Software. |
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* |
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, |
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF |
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND |
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE |
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* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION |
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* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION |
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. |
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* |
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*/ |
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/** |
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* @fileoverview A-Law codec. |
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* @see https://github.com/rochars/wavefile |
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* @see https://github.com/rochars/alawmulaw |
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*/ |
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/** @type {!Array<number>} */ |
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const LOG_TABLE = [ |
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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, |
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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, |
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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, |
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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 |
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]; |
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/** |
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* Encode a 16-bit linear PCM sample as 8-bit A-Law. |
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* @param {number} sample A 16-bit PCM sample |
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* @return {number} |
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*/ |
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export function encodeSample(sample) { |
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/** @type {number} */ |
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let compandedValue; |
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sample = (sample ==-32768) ? -32767 : sample; |
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/** @type {number} */ |
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let sign = ((~sample) >> 8) & 0x80; |
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if (!sign) { |
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sample = sample * -1; |
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} |
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if (sample > 32635) { |
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sample = 32635; |
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} |
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if (sample >= 256) { |
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/** @type {number} */ |
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let exponent = LOG_TABLE[(sample >> 8) & 0x7F]; |
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/** @type {number} */ |
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let mantissa = (sample >> (exponent + 3) ) & 0x0F; |
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compandedValue = ((exponent << 4) | mantissa); |
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} else { |
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compandedValue = sample >> 4; |
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} |
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return compandedValue ^ (sign ^ 0x55); |
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} |
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/** |
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* Decode a 8-bit A-Law sample as 16-bit PCM. |
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* @param {number} aLawSample The 8-bit A-Law sample |
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* @return {number} |
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*/ |
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export function decodeSample(aLawSample) { |
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/** @type {number} */ |
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let sign = 0; |
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aLawSample ^= 0x55; |
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if ((aLawSample & 0x80) !== 0) { |
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aLawSample &= ~(1 << 7); |
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sign = -1; |
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} |
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/** @type {number} */ |
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let position = ((aLawSample & 0xF0) >> 4) + 4; |
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/** @type {number} */ |
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let decoded = 0; |
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if (position != 4) { |
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decoded = ((1 << position) | |
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((aLawSample & 0x0F) << (position - 4)) | |
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(1 << (position - 5))); |
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} else { |
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decoded = (aLawSample << 1)|1; |
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} |
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decoded = (sign === 0) ? (decoded) : (-decoded); |
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return (decoded * 8) * -1; |
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} |
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/** |
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* Encode 16-bit linear PCM samples as 8-bit A-Law samples. |
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* @param {!Int16Array} samples A array of 16-bit PCM samples. |
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* @return {!Uint8Array} |
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*/ |
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export function encode(samples) { |
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/** @type {!Uint8Array} */ |
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let aLawSamples = new Uint8Array(samples.length); |
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for (let i = 0, len = samples.length; i < len; i++) { |
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aLawSamples[i] = encodeSample(samples[i]); |
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} |
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return aLawSamples; |
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} |
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/** |
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* Decode 8-bit A-Law samples into 16-bit linear PCM samples. |
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* @param {!Uint8Array} samples A array of 8-bit A-Law samples. |
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* @return {!Int16Array} |
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*/ |
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export function decode(samples) { |
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/** @type {!Int16Array} */ |
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let pcmSamples = new Int16Array(samples.length); |
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for (let i = 0, len = samples.length; i < len; i++) { |
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pcmSamples[i] = decodeSample(samples[i]); |
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} |
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return pcmSamples; |
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} |
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rochars /
wavefile
