julius_converter.js

var Converter = function(rate, bufferSize, byteSize) {
  this.rate = rate;
  this.bufferSize = bufferSize;
  this.byteSize = byteSize;

  // https://github.com/grantgalitz/XAudioJS/blob/master/resampler.js
  this.resampler = new Resampler(44100, rate, 1, bufferSize, true);
};

Converter.prototype.convert = (function() {
  // Helper functions to convert to PCM16=
  function f32Toi16(float) {
    // Guard against overflow
    var s = Math.max(-1, Math.min(1, float));
    // Assume 2's complement representation
    return s < 0 ? 0xFFFF ^ Math.floor(-s * 0x7FFF) : Math.floor(s * 0x7FFF);
  }
  function i16ToUTF8Array(i16, littleEndian) {
    var l = i16 >> 8;
    var r = i16 - (l << 8);
    return littleEndian ? [r, l] : [l, r];
  }

  return function(inp, out, ptr) {
    // Use Uint8Array to enforce endianness
    // TODO: use Int16Array TypedArray to enforce system endianness
    var buffer = new Uint8Array(out, ptr, this.byteSize);
    var l = this.resampler.resampler(inp);
    for (var i = 0; i < l; i++) {
      i16ToUTF8Array(f32Toi16(this.resampler.outputBuffer[i]), true)
        .forEach(function(val, ind) {
          buffer[i * 2 + ind] = val;
        });
    }
  };
}() );