feat: add useSilenceDetector composable with Web Audio API amplitude monitoring

frontend/src/composables/useSilenceDetector.ts

@@ -0,0 +1,66 @@
+import { ref, readonly } from 'vue'
+
+export interface SilenceDetectorOptions {
+  thresholdDb?: number       // default -40
+  silenceDurationMs?: number // default 1500
+  minRecordingMs?: number    // default 500
+}
+
+export function useSilenceDetector(options: SilenceDetectorOptions = {}) {
+  const {
+    thresholdDb = -40,
+    silenceDurationMs = 1500,
+    minRecordingMs = 500,
+  } = options
+
+  const amplitude = ref(0)
+  let audioCtx: AudioContext | null = null
+  let intervalId: ReturnType<typeof setInterval> | null = null
+  let silenceMs = 0
+  let startedAt = 0
+
+  function start(stream: MediaStream, onSilence: () => void): void {
+    stop()
+    audioCtx = new AudioContext()
+    const source = audioCtx.createMediaStreamSource(stream)
+    const analyser = audioCtx.createAnalyser()
+    analyser.fftSize = 256
+    source.connect(analyser)
+
+    const data = new Uint8Array(analyser.frequencyBinCount)
+    silenceMs = 0
+    startedAt = Date.now()
+
+    intervalId = setInterval(() => {
+      analyser.getByteFrequencyData(data)
+      const rms = Math.sqrt(data.reduce((s, v) => s + v * v, 0) / data.length) / 255
+      amplitude.value = rms
+
+      const db = rms > 0 ? 20 * Math.log10(rms) : -100
+      if (db < thresholdDb) {
+        silenceMs += 100
+        if (silenceMs >= silenceDurationMs && Date.now() - startedAt >= minRecordingMs) {
+          stop()
+          onSilence()
+        }
+      } else {
+        silenceMs = 0
+      }
+    }, 100)
+  }
+
+  function stop(): void {
+    if (intervalId !== null) {
+      clearInterval(intervalId)
+      intervalId = null
+    }
+    if (audioCtx) {
+      audioCtx.close().catch(() => {})
+      audioCtx = null
+    }
+    amplitude.value = 0
+    silenceMs = 0
+  }
+
+  return { amplitude: readonly(amplitude), start, stop }
+}