audiobuffer/lib/AudioBuffer.js

An implementation of Web Audio API's AudioBuffer for node.js and the browser.

var _ = require('underscore')

var AudioBuffer = module.exports = function(numberOfChannels, length, sampleRate) {
  var ch
  this._data = []
  // Just a hack to be able to create a partially initialized AudioBuffer
  if (arguments.length) {
    for (ch = 0; ch < numberOfChannels; ch++)
      this._data.push(new Float32Array(length))
    this._defineAttrs(numberOfChannels, length, sampleRate)
  }
}

_.extend(AudioBuffer.prototype, {

  getChannelData: function(channel) {
    if (channel >= this.numberOfChannels) throw new Error('invalid channel')
    return this._data[channel]
  },

  slice: function() {
    var sliceArgs = _.toArray(arguments)
      , array = this._data.map(function(chArray) {
        return chArray.slice.apply(chArray, sliceArgs)
      })
    return AudioBuffer.fromArray(array, this.sampleRate)
  },

  concat: function(other) {
    if (other.sampleRate !== this.sampleRate)
      throw new Error('the 2 AudioBuffers don\'t have the same sampleRate')
    if (other.numberOfChannels !== this.numberOfChannels)
      throw new Error('the 2 AudioBuffers don\'t have the same numberOfChannels')
    var newLength = other.length + this.length
      , newChArray
      , newArray = this._data.map(function(chArray, ch) {
        newChArray = new Float32Array(newLength)
        newChArray.set(chArray)
        newChArray.set(other._data[ch], chArray.length)
        return newChArray
      })
    return AudioBuffer.fromArray(newArray, this.sampleRate)
  },

  set: function(other, offset) {
    if (other.sampleRate !== this.sampleRate)
      throw new Error('the 2 AudioBuffers don\'t have the same sampleRate')
    if (other.numberOfChannels !== this.numberOfChannels)
      throw new Error('the 2 AudioBuffers don\'t have the same numberOfChannels')
    this._data.forEach(function(chArray, ch) {
      chArray.set(other.getChannelData(ch), offset)
    })
  },

  _defineAttrs: function(numberOfChannels, length, sampleRate) {
    if (!(sampleRate > 0)) throw new Error('invalid sample rate : ' + sampleRate)
    Object.defineProperty(this, 'sampleRate', {value: sampleRate, writable: false})
    if (!(length >= 0)) throw new Error('invalid length : ' + length)
    Object.defineProperty(this, 'length', {value: length, writable: false})
    Object.defineProperty(this, 'duration', {value: length / sampleRate, writable: false})
    if (!(numberOfChannels > 0)) throw new Error('invalid numberOfChannels : ' + numberOfChannels)
    Object.defineProperty(this, 'numberOfChannels', {value: numberOfChannels, writable: false})
  }

})

// -------------------- Class attributes -------------------- //
_.extend(AudioBuffer, {

  filledWithVal: function(val, numberOfChannels, length, sampleRate) {
    var audioBuffer = new AudioBuffer(numberOfChannels, length, sampleRate)
      , chData, ch, i
    for (ch = 0; ch < numberOfChannels; ch++) {
      chData = audioBuffer._data[ch]
      for (i = 0; i < length; i++) chData[i] = val
    }
    return audioBuffer
  },

  fromArray: function(array, sampleRate) {
    var audioBuffer = new AudioBuffer()
    audioBuffer._defineAttrs(array.length, array[0].length, sampleRate)
    array.forEach(function(chArray) {
      if (!(chArray instanceof Float32Array))
        chArray = new Float32Array(chArray)
      audioBuffer._data.push(chArray)
    })
    return audioBuffer
  }

})