rochars / bitdepth

 * 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/bitdepth

 */

/** @module 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);

  // FP to int need the original samples to be clipped

  // at 1 and -1 as files can have samples out of those boundaries

  if (["32f","64"].indexOf(bithDepth) > -1) {

    truncateSamples_(samples);

  }

  // change the resolution of the samples

  for (let i = 0; i< samples.length; 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

 */

/**

 * 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.");

  }

}

/**

 * Truncate float samples on overflow.

 * @param {!Array|!TypedArray} samples The samples.

 * @private

 */

function truncateSamples_(samples) {

  /** @type {number} */   

  let len = samples.length;

  for (let i=0; i<len; i++) {

    if (samples[i] > 1) {

      samples[i] = 1;

    } else if (samples[i] < -1) {

      samples[i] = -1;

    }

  }

}

/**

 * 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; i < samples.length; i++) {

      samples[i] = samples[i] += factor;

    }

  }

}