1 files changed, 60 insertions, 0 deletions
diff --git a/static/mic-worklet.js b/static/mic-worklet.js
new file mode 100644
index 0000000..814bf6a
--- /dev/null
+++ b/static/mic-worklet.js
@@ -0,0 +1,60 @@
+// 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);