static/mic-worklet.js


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// Microphone capture worklet: resamples the context rate to 48 kHz mono and
// posts 20 ms frames (960 Float32 samples) together with their RMS level.
const OUT_RATE = 48000;
const FRAME_SAMPLES = 960;

class Ts6MicCapture extends AudioWorkletProcessor {
  constructor() {
    super();
    this.ratio = sampleRate / OUT_RATE; // input samples per output sample
    this.t = 0;      // fractional read position; -1 refers to `last`
    this.last = 0;
    this.frame = new Float32Array(FRAME_SAMPLES);
    this.offset = 0;
  }

  push(sample) {
    this.frame[this.offset++] = sample;
    if (this.offset < FRAME_SAMPLES) return;
    let sum = 0;
    for (let i = 0; i < FRAME_SAMPLES; i++) sum += this.frame[i] * this.frame[i];
    const frame = this.frame;
    this.frame = new Float32Array(FRAME_SAMPLES);
    this.offset = 0;
    this.port.postMessage({ samples: frame, rms: Math.sqrt(sum / FRAME_SAMPLES) }, [frame.buffer]);
  }

  process(inputs, outputs) {
    const output = outputs[0] && outputs[0][0];
    if (output) output.fill(0);
    const channels = inputs[0];
    if (!channels || channels.length === 0) return true;

    // Downmix to mono.
    let input = channels[0];
    if (channels.length > 1) {
      input = new Float32Array(input.length);
      for (const ch of channels) for (let i = 0; i < input.length; i++) input[i] += ch[i] / channels.length;
    }

    if (this.ratio === 1) {
      for (let i = 0; i < input.length; i++) this.push(input[i]);
      return true;
    }
    // Linear interpolation resampler.
    const len = input.length;
    while (this.t < len - 1) {
      const i0 = Math.floor(this.t);
      const frac = this.t - i0;
      const a = i0 < 0 ? this.last : input[i0];
      const b = input[i0 + 1];
      this.push(a + (b - a) * frac);
      this.t += this.ratio;
    }
    this.t -= len;
    this.last = input[len - 1];
    return true;
  }
}

registerProcessor("ts6-mic-capture", Ts6MicCapture);