feat(voice): harden Gemini Live provider integration

src/voice/geminiCaptureWorklet.js

@@ -0,0 +1,125 @@
+const OUTPUT_RATE = 16000;
+const FILTER_TAPS = 64;
+const FILTER_PHASES = 128;
+
+// A causal, windowed-sinc low-pass filter avoids folding device frequencies
+// above 8 kHz into speech. Precompute phases; process allocates no filter data.
+function resamplingFilters(inputRate) {
+  const cutoff = 0.45 * Math.min(1, OUTPUT_RATE / inputRate);
+  const filters = new Float32Array(FILTER_TAPS * FILTER_PHASES);
+  for (let phase = 0; phase < FILTER_PHASES; phase++) {
+    let total = 0;
+    for (let tap = 0; tap < FILTER_TAPS; tap++) {
+      const distance = tap - (FILTER_TAPS - 1) / 2 - phase / FILTER_PHASES;
+      const sinc =
+        distance === 0
+          ? 2 * cutoff
+          : Math.sin(2 * Math.PI * cutoff * distance) / (Math.PI * distance);
+      const window =
+        0.5 - 0.5 * Math.cos((2 * Math.PI * tap) / (FILTER_TAPS - 1));
+      const weight = sinc * window;
+      filters[phase * FILTER_TAPS + tap] = weight;
+      total += weight;
+    }
+    for (let tap = 0; tap < FILTER_TAPS; tap++)
+      filters[phase * FILTER_TAPS + tap] /= total;
+  }
+  return filters;
+}
+
+/** PCM microphone capture. Only explicitly enabled frames leave this processor. */
+class GeminiCaptureProcessor extends AudioWorkletProcessor {
+  constructor() {
+    super();
+    this.enabled = false;
+    this.captureId = null;
+    this.samples = new Int16Array(1024);
+    this.length = 0;
+    this.inputRate = sampleRate;
+    this.filters =
+      this.inputRate === OUTPUT_RATE ? null : resamplingFilters(this.inputRate);
+    this.history = new Float32Array(FILTER_TAPS);
+    this.resetResampler();
+    this.port.onmessage = ({ data }) => {
+      if (data?.enabled === true) {
+        if (
+          this.enabled ||
+          !Number.isSafeInteger(data.captureId) ||
+          data.captureId <= 0
+        )
+          return;
+        this.captureId = data.captureId;
+        this.resetResampler();
+        this.enabled = true;
+        this.port.postMessage({ type: 'start', captureId: this.captureId });
+      } else if (
+        data?.enabled === false &&
+        this.enabled &&
+        data.captureId === this.captureId
+      ) {
+        this.flush();
+        this.port.postMessage({ type: 'end', captureId: this.captureId });
+        this.enabled = false;
+        this.captureId = null;
+        this.length = 0;
+        // Do not drain filter tails into a later physical microphone capture.
+        this.resetResampler();
+      }
+    };
+  }
+  resetResampler() {
+    this.phase = 0;
+    this.historyIndex = 0;
+    this.history.fill(0);
+  }
+  appendSample(sample) {
+    const value = Math.max(-1, Math.min(1, sample));
+    this.samples[this.length++] = Math.round(
+      value * (value < 0 ? 32768 : 32767),
+    );
+    if (this.length === this.samples.length) this.flush();
+  }
+  flush() {
+    if (!this.length) return;
+    const buffer = new ArrayBuffer(this.length * 2);
+    const view = new DataView(buffer);
+    for (let i = 0; i < this.length; i++)
+      view.setInt16(i * 2, this.samples[i], true);
+    this.port.postMessage(
+      { type: 'audio', buffer, captureId: this.captureId },
+      [buffer],
+    );
+    this.length = 0;
+  }
+  process(inputs) {
+    if (!this.enabled) return true;
+    const channel = inputs[0]?.[0];
+    if (!channel) return true;
+    for (const sample of channel) {
+      if (!this.filters) {
+        this.appendSample(sample);
+        continue;
+      }
+      this.history[this.historyIndex] = sample;
+      this.historyIndex = (this.historyIndex + 1) % FILTER_TAPS;
+      this.phase += OUTPUT_RATE;
+      while (this.phase >= this.inputRate) {
+        this.phase -= this.inputRate;
+        const phase = Math.min(
+          FILTER_PHASES - 1,
+          Math.floor((this.phase * FILTER_PHASES) / OUTPUT_RATE),
+        );
+        let value = 0;
+        for (let tap = 0; tap < FILTER_TAPS; tap++) {
+          const index =
+            (this.historyIndex - 1 - tap + FILTER_TAPS) % FILTER_TAPS;
+          value +=
+            this.history[index] * this.filters[phase * FILTER_TAPS + tap];
+        }
+        this.appendSample(value);
+      }
+    }
+    return true;
+  }
+}
+registerProcessor('gev-gemini-capture', GeminiCaptureProcessor);