AudioWorklet

// datei: noise-processor.js (läuft im AudioWorkletGlobalScope)
class NoiseProcessor extends AudioWorkletProcessor {
  static get parameterDescriptors() {
    return [{ name: 'gain', defaultValue: 0.2, minValue: 0, maxValue: 1 }];
  }

  process(inputs, outputs, parameters) {
    const output = outputs[0];
    const gain = parameters.gain;
    for (const channel of output) {
      for (let i = 0; i < channel.length; i++) {
        // Der Parameter kann ein Wert pro Block oder pro Sample sein
        const g = gain.length > 1 ? gain[i] : gain[0];
        channel[i] = (Math.random() * 2 - 1) * g;
      }
    }
    return true; // Prozessor aktiv halten
  }
}

registerProcessor('noise-processor', NoiseProcessor);

// Haupt-Thread, z. B. in einem Klick-Handler (Autoplay-Richtlinie)
const startButton = document.querySelector('#start');

startButton.addEventListener('click', async () => {
  const ctx = new AudioContext();
  await ctx.audioWorklet.addModule('noise-processor.js');

  const noise = new AudioWorkletNode(ctx, 'noise-processor');
  noise.connect(ctx.destination);

  // Lautstärke über den AudioParam sanft ändern
  const gain = noise.parameters.get('gain');
  gain.setValueAtTime(0.2, ctx.currentTime);
  gain.linearRampToValueAtTime(0, ctx.currentTime + 2);

  console.log('Rauschen läuft, Samplerate:', ctx.sampleRate);
});

// Prozessor-Code als Blob-URL, damit keine eigene Datei nötig ist
const code = `
class MeterProcessor extends AudioWorkletProcessor {
  constructor() { super(); this.frames = 0; }
  process(inputs) {
    const input = inputs[0][0];
    if (input) {
      let sum = 0;
      for (const s of input) sum += s * s;
      this.frames += input.length;
      if (this.frames >= sampleRate / 10) { // etwa 10-mal pro Sekunde
        this.port.postMessage(Math.sqrt(sum / input.length));
        this.frames = 0;
      }
    }
    return true;
  }
}
registerProcessor('meter', MeterProcessor);`;

const url = URL.createObjectURL(new Blob([code], { type: 'application/javascript' }));

const startMeter = async () => {
  const ctx = new AudioContext();
  await ctx.audioWorklet.addModule(url);
  const stream = await navigator.mediaDevices.getUserMedia({ audio: true });
  const mic = ctx.createMediaStreamSource(stream);
  const meter = new AudioWorkletNode(ctx, 'meter');
  meter.port.onmessage = ({ data }) => console.log('RMS:', data.toFixed(3));
  mic.connect(meter);
};

startMeter();