prx-wavefile/lib/codecs/bitdepth.js

Create, read and write wav files according to the specs.

/*
 * Copyright (c) 2017-2018 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 module to change the bit depth of PCM samples.
 * @see https://github.com/rochars/wavefile
 * @see https://github.com/rochars/bitdepth
 */

/**
 * Change the bit depth of PCM samples.
 * @param {!Array|!TypedArray} samples The original samples.
 * @param {string} bithDepth The original bit depth.
 * @param {!TypedArray} newSamples The output array.
 * @param {string} targetBitDepth The target bit depth.
 * @throws {Error} If original or target bit depths are not valid.
 */
export function changeBitDepth(samples, bithDepth, newSamples, targetBitDepth) {
  // float to float, just copy the values
  if (["32f","64"].indexOf(bithDepth) > -1 &&
    ["32f","64"].indexOf(targetBitDepth) > -1) {
    newSamples.set(samples);
    return;
  }
  validateBitDepth_(bithDepth);
  validateBitDepth_(targetBitDepth);
  /** @type {!Function} */
  let toFunction = getBitDepthFunction_(bithDepth, targetBitDepth);
  /** @type {!Object<string, number>} */
  let options = {
    oldMin: Math.pow(2, parseInt(bithDepth, 10)) / 2,
    newMin: Math.pow(2, parseInt(targetBitDepth, 10)) / 2,
    oldMax: (Math.pow(2, parseInt(bithDepth, 10)) / 2) - 1,
    newMax: (Math.pow(2, parseInt(targetBitDepth, 10)) / 2) - 1,
  };
  // sign the samples if original is 8-bit
  sign8Bit_(bithDepth, samples, true);
  // change the resolution of the samples
  for (let i = 0, len = samples.length; i < len; i++) {        
    newSamples[i] = toFunction(samples[i], options);
  }
  // unsign the samples if target is 8-bit
  sign8Bit_(targetBitDepth, newSamples, false);
}

/**
 * Change the bit depth from int to int.
 * @param {number} sample The sample.
 * @param {!Object<string, number>} args Data about the bit depths.
 * @return {number}
 * @private
 */
function intToInt_(sample, args) {
  if (sample > 0) {
    sample = parseInt((sample / args.oldMax) * args.newMax, 10);
  } else {
    sample = parseInt((sample / args.oldMin) * args.newMin, 10);
  }
  return sample;
}

/**
 * Change the bit depth from float to int.
 * @param {number} sample The sample.
 * @param {!Object<string, number>} args Data about the bit depths.
 * @return {number}
 * @private
 */
function floatToInt_(sample, args) {
  return parseInt(
    sample > 0 ? sample * args.newMax : sample * args.newMin, 10);
}

/**
 * Change the bit depth from int to float.
 * @param {number} sample The sample.
 * @param {!Object<string, number>} args Data about the bit depths.
 * @return {number}
 * @private
 */
function intToFloat_(sample, args) {
  return sample > 0 ? sample / args.oldMax : sample / args.oldMin;
}

/**
 * Return the function to change the bit depth of a sample.
 * @param {string} original The original bit depth of the data.
 * @param {string} target The new bit depth of the data.
 * @return {!Function}
 * @private
 */
function getBitDepthFunction_(original, target) {
  /** @type {!Function} */
  let func = function(x) {return x;};
  if (original != target) {
    if (["32f", "64"].includes(original)) {
      func = floatToInt_;
    } else {
      if (["32f", "64"].includes(target)) {
        func = intToFloat_;
      } else {
        func = intToInt_;
      }
    }
  }
  return func;
}

/**
 * Validate the bit depth.
 * @param {string} bitDepth The original bit depth.
 * @throws {Error} If bit depth is not valid.
 * @private
 */
function validateBitDepth_(bitDepth) {
  if ((bitDepth != "32f" && bitDepth != "64") &&
      (parseInt(bitDepth, 10) < "8" || parseInt(bitDepth, 10) > "53")) {
    throw new Error("Invalid bit depth.");
  }
}

/**
 * Sign samples if they are 8-bit.
 * @param {string} bitDepth The bit depth code.
 * @param {!Array|!TypedArray} samples The samples.
 * @param {boolean} sign True to sign, false to unsign.
 * @private
 */
function sign8Bit_(bitDepth, samples, sign) {
  if (bitDepth == "8") {
    let factor = sign ? -128 : 128;
    for (let i = 0, len = samples.length; i < len; i++) {
      samples[i] = samples[i] += factor;
    }
  }
}