ES5 AudioWorklet Processor

recorder-processor.js

function RecorderProcessor(options) {
  AudioWorkletProcessor.call(this);

  var processorOptions = options.processorOptions || {};
  this.numInputChannels = processorOptions.numInputChannels || 2;
  this.recording = false;

  this.clear();

  this.port.onmessage = function(event) {
    var data = event.data;
    if (data.name === 'start') {
      this.record(data.duration);
    } else if (data.name === 'stop') {
      this.stop();
    }
  }.bind(this);
}

RecorderProcessor.prototype = Object.create(AudioWorkletProcessor.prototype);
RecorderProcessor.prototype.constructor = RecorderProcessor;

RecorderProcessor.prototype.process = function(inputs, outputs) {
  if (!this.recording) {
    return true;
  } else if (this.sampleLimit && this.recordedSamples >= this.sampleLimit) {
    this.stop();
  }

  var input = inputs[0];
  var output = outputs[0];

  for (var channel = 0; channel < output.length; ++channel) {
    var inputChannel = input[channel];
    if (channel === 0) {
      this.leftBuffers.push(inputChannel);
      if (this.numInputChannels === 1) {
        this.rightBuffers.push(inputChannel);
      }
    } else if (channel === 1 && this.numInputChannels > 1) {
      this.rightBuffers.push(inputChannel);
    }
  }

  this.recordedSamples += output[0].length;

  return true;
};

RecorderProcessor.prototype.record = function(duration) {
  if (duration) {
    this.sampleLimit = Math.round(duration * sampleRate);
  }
  this.recording = true;
};

RecorderProcessor.prototype.stop = function() {
  this.recording = false;
  const buffers = this.getBuffers();
  const leftBuffer = buffers[0].buffer;
  const rightBuffer = buffers[1].buffer;
  this.port.postMessage(
    {
      name: 'buffers',
      leftBuffer: leftBuffer,
      rightBuffer: rightBuffer
    },
    [leftBuffer, rightBuffer]
  );
  this.clear();
};

RecorderProcessor.prototype.getBuffers = function() {
  var buffers = [];
  buffers.push(this.mergeBuffers(this.leftBuffers));
  buffers.push(this.mergeBuffers(this.rightBuffers));
  return buffers;
};

RecorderProcessor.prototype.mergeBuffers = function(channelBuffer) {
  var result = new Float32Array(this.recordedSamples);
  var offset = 0;
  var lng = channelBuffer.length;
  for (var i = 0; i < lng; i++) {
    var buffer = channelBuffer[i];
    result.set(buffer, offset);
    offset += buffer.length;
  }
  return result;
};

RecorderProcessor.prototype.clear = function() {
  this.leftBuffers = [];
  this.rightBuffers = [];
  this.recordedSamples = 0;
  this.sampleLimit = null;
};