volume-processor.js

const SMOOTHING_FACTOR = 0.8;
const MINIMUM_VALUE = 0.00001;

// This is the way to register an AudioWorkletProcessor
// it's necessary to declare a name, in this case
// the name is "vumeter"
registerProcessor('volume', class extends AudioWorkletProcessor {

  //_volume
  _updateIntervalInMS
  _nextUpdateFrame

  constructor () {
    super();
    //this._volume = 0;
    this._updateIntervalInMS = 40; // analyse 25 times per second (.onaudioprocess occurs between 23 and 24 times a seocnd)
    this._nextUpdateFrame = this._updateIntervalInMS;
    /*this.port.onmessage = event => {
      if (event.data.updateIntervalInMS)
        this._updateIntervalInMS = event.data.updateIntervalInMS;
    }*/
  }

  get intervalInFrames () {
    return this._updateIntervalInMS / 1000 * sampleRate;
  }

  process (inputs, outputs, parameters) {
    const input = inputs[0];

    // Note that the input will be down-mixed to mono; however, if no inputs are
    // connected then zero channels will be passed in.
    if (input.length > 0) {
      const samples = input[0];
      let sum = 0, i = 0;
      let rms = 0;

      // Calculated the squared-sum.
      while (i < samples.length) sum += Math.abs(samples[i++]);

      // Calculate the RMS level and update the volume.
      rms = Math.sqrt(sum / samples.length);
      

      // Update and sync the volume property with the main thread.
      this._nextUpdateFrame -= samples.length;
      if (this._nextUpdateFrame < 0) {
        this._nextUpdateFrame += this.intervalInFrames;
        this.port.postMessage({rms: rms}); // If we remove the if-condition, this happens 380x per second
      }
    }
    
    return true;
  }
});