code: function FOARouter(context, channelMap) {
    this._context = context;
  
    this._splitter = this._context.createChannelSplitter(4);
    this._merger = this._context.createChannelMerger(4);
  
    // input/output proxy.
    this.input = this._splitter;
    this.output = this._merger;
  
    this.setChannelMap(channelMap || ChannelMap.DEFAULT);
  }
docs: Channel router for FOA stream.
  @constructor
  @param {AudioContext} context - Associated AudioContext.
  @param {Number[]} channelMap - Routing destination array.