web-audio-api/lib/audioports.js

Node.js implementation of Web audio API

var _ = require('underscore')
  , async = require('async')
  , events = require('events')
  , utils = require('./utils')
  , AudioBuffer = require('./AudioBuffer')
  , BLOCK_SIZE = require('./constants').BLOCK_SIZE
  , ChannelMixing = require('./ChannelMixing')


class AudioPort extends events.EventEmitter {

  constructor(context, node, id) {
    super()
    this.connections = []
    this.node = node
    this.id = id
    this.context = context
  }

  // Generic function for connecting the calling AudioPort
  // with `otherPort`. Returns true if a connection was indeed established
  connect(otherPort) {
    if (this.connections.indexOf(otherPort) !== -1) return false
    this.connections.push(otherPort)
    otherPort.connect(this)
    this.emit('connection', otherPort)
    return true
  }

  // Generic function for disconnecting the calling AudioPort
  // from `otherPort`. Returns true if a disconnection was indeed made
  disconnect(otherPort) {
    var connInd = this.connections.indexOf(otherPort)
    if (connInd === -1) return false
    this.connections.splice(connInd, 1)
    otherPort.disconnect(this)
    this.emit('disconnection', otherPort)
    return true
  }

  // Called when a node is killed. Removes connections, and event listeners.
  _kill() {
    this.connections.slice(0).forEach((port) => {
      this.disconnect(port)
    })
    this.removeAllListeners()
  }

}

class AudioInput extends AudioPort {

  constructor(context, node, id) {
    super(context, node, id)

    // `computedNumberOfChannels` is scheduled to be recalculated everytime a connection
    // or disconnection happens.
    this.computedNumberOfChannels = null
    this.on('connected', () => {
      this.computedNumberOfChannels = null
    })
    this.on('disconnected', () => {
      this.computedNumberOfChannels = null
    })

    // Just for code clarity
    Object.defineProperty(this, 'sources', {
      get: function() {
        return this.connections
      }
    })
  }

  connect(source) {
    // When the number of channels of the source changes, we trigger
    // computation of `computedNumberOfChannels`
    source.on('_numberOfChannels', () => {
      this.computedNumberOfChannels = null
    })
    //AudioPort.prototype.connect.call(this, source)
    super.connect(source)
  }

  disconnect(source) {
    source.removeAllListeners('_numberOfChannels')
    //AudioPort.prototype.disconnect.call(this, source)
    super.disconnect(source)
  }

  _tick() {
    var i, ch, inNumChannels, inBuffers = this.sources.map(function(source) {
      return source._tick()
    })

    if (this.computedNumberOfChannels === null) {
      var maxChannelsUpstream
      if (this.sources.length) {
        maxChannelsUpstream = _.chain(inBuffers).pluck('numberOfChannels').max().value()
      } else maxChannelsUpstream = 0
      this._computeNumberOfChannels(maxChannelsUpstream)
    }
    var outBuffer = new AudioBuffer(this.computedNumberOfChannels, BLOCK_SIZE, this.context.sampleRate)

    inBuffers.forEach((inBuffer) => {
      var ch = new ChannelMixing(inBuffer.numberOfChannels, this.computedNumberOfChannels, this.node.channelInterpretation)
      ch.process(inBuffer, outBuffer)
    })
    return outBuffer
  }

  _computeNumberOfChannels(maxChannelsUpstream) {
    var countMode = this.node.channelCountMode,
      channelCount = this.node.channelCount
    maxChannelsUpstream = maxChannelsUpstream || 1

    if (countMode === 'max') {
      this.computedNumberOfChannels = maxChannelsUpstream
    } else if (countMode === 'clamped-max') {
      this.computedNumberOfChannels = Math.min(maxChannelsUpstream, channelCount)
    } else if (countMode === 'explicit')
      this.computedNumberOfChannels = channelCount
      // this shouldn't happen
    else throw new Error('invalid channelCountMode')
  }

}

class AudioOutput extends AudioPort {

  constructor(context, node, id) {
    super(context, node, id)

    // This caches the block fetched from the node.
    this._cachedBlock = {
      time: -1,
      buffer: null
    }

    // This catches the number of channels of the audio going through this output
    this._numberOfChannels = null

    // Just for code clarity
    Object.defineProperty(this, 'sinks', {
      get: function() {
        return this.connections
      }
    })
  }

  // Pulls the audio from the node only once, and copies it so that several
  // nodes downstream can pull the same block.
  _tick() {
    if (this._cachedBlock.time < this.context.currentTime) {
      var outBuffer = this.node._tick()
      if (this._numberOfChannels !== outBuffer.numberOfChannels) {
        this._numberOfChannels = outBuffer.numberOfChannels
        this.emit('_numberOfChannels')
      }
      this._cachedBlock = {
        time: this.context.currentTime,
        buffer: outBuffer
      }
      return outBuffer
    } else return this._cachedBlock.buffer
  }

}

module.exports = {
  AudioOutput: AudioOutput,
  AudioInput: AudioInput
}