index.js

var AudioContext = window.AudioContext || window.webkitAudioContext

module.exports = WebAudioAnalyser

function WebAudioAnalyser(audio, ctx, opts) {
  if (!(this instanceof WebAudioAnalyser)) return new WebAudioAnalyser(audio, ctx, opts)
  if (!(ctx instanceof AudioContext)) (opts = ctx), (ctx = null)

  opts = opts || {}
  this.ctx = ctx = ctx || new AudioContext

  if (!(audio instanceof AudioNode)) {
    audio = (audio instanceof Audio || audio instanceof HTMLAudioElement)
      ? ctx.createMediaElementSource(audio)
      : ctx.createMediaStreamSource(audio)
  }

  this.analyser = ctx.createAnalyser()
  this.stereo   = !!opts.stereo
  this.audible  = opts.audible !== false
  this.wavedata = null
  this.freqdata = null
  this.splitter = null
  this.merger   = null
  this.source   = audio

  if (!this.stereo) {
    this.output = this.source
    this.source.connect(this.analyser)
    if (this.audible)
      this.analyser.connect(ctx.destination)
  } else {
    this.analyser = [this.analyser]
    this.analyser.push(ctx.createAnalyser())

    this.splitter = ctx.createChannelSplitter(2)
    this.merger   = ctx.createChannelMerger(2)
    this.output   = this.merger

    this.source.connect(this.splitter)

    for (var i = 0; i < 2; i++) {
      this.splitter.connect(this.analyser[i], i, 0)
      this.analyser[i].connect(this.merger, 0, i)
    }

    if (this.audible)
      this.merger.connect(ctx.destination)
  }
}

WebAudioAnalyser.prototype.waveform = function(output, channel) {
  if (!output) output = this.wavedata || (
    this.wavedata = new Uint8Array((this.analyser[0] || this.analyser).frequencyBinCount)
  )

  var analyser = this.stereo
    ? this.analyser[channel || 0]
    : this.analyser

  analyser.getByteTimeDomainData(output)

  return output
}

WebAudioAnalyser.prototype.frequencies = function(output, channel) {
  if (!output) output = this.freqdata || (
    this.freqdata = new Uint8Array((this.analyser[0] || this.analyser).frequencyBinCount)
  )

  var analyser = this.stereo
    ? this.analyser[channel || 0]
    : this.analyser

  analyser.getByteFrequencyData(output)

  return output
}