recorderProcessor.js

// import processor name via preval.require so that it's available as a value at compile time
const processorNames = preval.require('./processorNames');

class RecorderProcessor extends AudioWorkletProcessor {
  constructor(options) {
    super();

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

    this.clear();

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

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

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

    for (let channel = 0; channel < output.length; ++channel) {
      const 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;
  }

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

  stop() {
    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();
  }

  getBuffers() {
    const buffers = [];
    buffers.push(this.mergeBuffers(this.leftBuffers));
    buffers.push(this.mergeBuffers(this.rightBuffers));
    return buffers;
  }

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

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

registerProcessor(processorNames.recorderProcessor, RecorderProcessor);