WaveWriter for JavaScript

gistfile1.js

/**
 * Creates a helper to write a WAVE file to a Buffer.
 * @param {Number} seconds - The length of the WAVE file to write.
 * @param {Number} sampleRate - The sample rate in Hz, such as 44100 for a CD.
 * @param {Number} bitsPerSample - Either 8 or 16.
 */
var WaveWriter = function(seconds, sampleRate, bitsPerSample) {
  this._sampleRate = sampleRate;
  this._bitsPerSample = bitsPerSample;
  this._writer = new BufferWriter();
  this._samples = Math.round(this._sampleRate * seconds);

  var numChannels = 1;
  var subChunk2Size = this._samples * numChannels * bitsPerSample / 8;
  var chunkSize = 36 + subChunk2Size;
  try {
    this._writer.writeUTF8("RIFF");
    this._writer.writeUInt32LE(chunkSize);
    this._writer.writeUTF8("WAVE");
  } catch (e1) {
    console.error("Got an exception while writing WAVE header.");
    throw e1;
  }

  try {
    // Sub-chunk 1
    var byteRate = 36 + sampleRate * numChannels * bitsPerSample / 8;
    var blockAlign = numChannels * bitsPerSample / 8;

    this._writer.writeUTF8("fmt ");
    this._writer.writeUInt32LE(16);
    this._writer.writeUInt16LE(1);
    this._writer.writeUInt16LE(numChannels);
    this._writer.writeUInt32LE(sampleRate);
    this._writer.writeUInt32LE(byteRate);
    this._writer.writeUInt16LE(blockAlign);
    this._writer.writeUInt16LE(bitsPerSample);
  } catch (e2) {
    console.error("Got an exception while writing subchunk 1.");
    throw e2;
  }

  try {
    // Sub-chunk 2
    this._writer.writeUTF8("data");
    this._writer.writeUInt32LE(subChunk2Size);
  } catch (e3) {
    console.error("Got an exception while writing subchunk 2.");
    throw e3;
  }
};

_.extend(WaveWriter.prototype, {
  /**
   * Write a single sample to the WAVE file.
   * @param {Number} sample The amplitude of the sample, from -1 to 1.
   * @return {Boolean} false if the file is already full, true otherwise.
   */
  writeSample: function(sample) {
    if (this._samples === 0) {
      return false;
    }
    // Clamp values out of range.
    if (sample < -1.0) {
      sample = -1;
    }
    if (sample > 1.0) {
      sample = 1;
    }
    if (this._bitsPerSample === 16) {
      this._writer.writeInt16(Math.floor(32767 * sample));
    } else if (this._bitsPerSample === 8) {
      try {
        this._writer.writeUInt8(Math.floor(-127.5 * sample + 127.5));
      } catch (e) {
        console.error("Got an exception while writing a sample.");
        console.error("Sample is " + Math.floor(-127.5 * sample + 127.5));
        throw e;
      }
    }
    this._samples = this._samples - 1;
    return true;
  },

  /**
   * Fills the rest of the file with zero-amplitude samples.
   */
  close: function() {
    while (this._samples > 0) {
      this.writeSample(0.0);
    }
  },

  /**
   * Returns the underlying buffer with the contents of the WAVE file.
   */
  buffer: function() {
    return this._writer.buffer();
  },
});