fix: switch VAD gate to per-frame probability control

onSpeechStart/onSpeechEnd fire at segment boundaries — with constant
non-speech noise, onSpeechEnd never fires so the gate stayed open.
Switch to onFrameProcessed which fires every ~96ms and applies hysteresis
(open at >0.5, close at <0.35) matching Silero's own thresholds. Gate now
starts closed and opens only once the first speech frame is confirmed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/livekit/SileroVADGate.ts

@@ -12,27 +12,34 @@ const log = logger.getChild("[SileroVADGate]");
 
 const VAD_BASE_PATH = "/vad/";
 
+// Speech probability above this value opens the gate; below it closes it.
+// vad-web's defaults are positiveSpeechThreshold=0.5, negativeSpeechThreshold=0.35.
+// We use those same values so the gate tracks the model's own speech/silence logic.
+const SPEECH_OPEN_THRESHOLD = 0.5;
+const SPEECH_CLOSE_THRESHOLD = 0.35;
+
 /**
- * Wraps @ricky0123/vad-web's MicVAD to feed speech/silence decisions into the
- * NoiseGateTransformer's VAD gate.  Instead of creating its own microphone
- * stream, it receives the existing LiveKit MediaStream so the VAD sees exactly
- * the same audio the worklet processes.
+ * Wraps @ricky0123/vad-web's MicVAD to feed per-frame speech probability
+ * decisions into the NoiseGateTransformer's VAD gate.
  *
- * Usage:
- *   const gate = new SileroVADGate(stream, audioContext);
- *   gate.onSpeechStart = () => transformer.setVADOpen(true);
- *   gate.onSpeechEnd   = () => transformer.setVADOpen(false);
- *   await gate.start();
- *   // later:
- *   await gate.destroy();
+ * Uses onFrameProcessed (fires every ~96ms) rather than the segment-level
+ * onSpeechStart/onSpeechEnd callbacks. The segment callbacks only fire at
+ * speech segment boundaries — with purely non-speech noise, onSpeechEnd
+ * never fires and the gate stays open. Per-frame probability control fixes
+ * this: the gate closes on the first silent frame.
+ *
+ * The gate starts closed (silent) and opens only once the VAD confirms speech.
  */
 export class SileroVADGate {
-  public onSpeechStart: () => void = () => {};
-  public onSpeechEnd: () => void = () => {};
+  /** Called each time the gate transitions to open (speech detected). */
+  public onOpen: () => void = () => {};
+  /** Called each time the gate transitions to closed (silence detected). */
+  public onClose: () => void = () => {};
 
   private vad: MicVAD | null = null;
   private readonly stream: MediaStream;
   private readonly audioContext: AudioContext;
+  private gateOpen = false;
 
   public constructor(stream: MediaStream, audioContext: AudioContext) {
     this.stream = stream;
@@ -57,21 +64,28 @@ export class SileroVADGate {
       pauseStream: async (): Promise<void> => {},
       // eslint-disable-next-line @typescript-eslint/require-await
       resumeStream: async (): Promise<MediaStream> => stream,
-      onSpeechStart: (): void => {
-        log.debug("speech start");
-        this.onSpeechStart();
+      onFrameProcessed: (probabilities: { isSpeech: number; notSpeech: number }): void => {
+        const p = probabilities.isSpeech;
+        if (!this.gateOpen && p >= SPEECH_OPEN_THRESHOLD) {
+          this.gateOpen = true;
+          log.debug("gate open (isSpeech=", p, ")");
+          this.onOpen();
+        } else if (this.gateOpen && p < SPEECH_CLOSE_THRESHOLD) {
+          this.gateOpen = false;
+          log.debug("gate close (isSpeech=", p, ")");
+          this.onClose();
+        }
       },
-      onSpeechEnd: (): void => {
-        log.debug("speech end");
-        this.onSpeechEnd();
-      },
-      onVADMisfire: (): void => {
-        log.debug("VAD misfire");
-      },
-      onFrameProcessed: (): void => {},
+      onSpeechStart: (): void => {},
+      onSpeechEnd: (): void => {},
+      onVADMisfire: (): void => {},
       onSpeechRealStart: (): void => {},
     });
 
+    // Gate starts closed — audio is muted until the first speech frame arrives.
+    this.gateOpen = false;
+    this.onClose();
+
     await this.vad.start();
     log.info("MicVAD started");
   }

src/state/CallViewModel/localMember/Publisher.ts

@@ -468,8 +468,10 @@ export class Publisher {
       }
       const stream = new MediaStream([rawTrack]);
       vadGate = new SileroVADGate(stream, ctx);
-      vadGate.onSpeechStart = (): void => transformer?.setVADOpen(true);
-      vadGate.onSpeechEnd = (): void => transformer?.setVADOpen(false);
+      // Close the gate immediately — VAD will open it once speech is confirmed.
+      transformer?.setVADOpen(false);
+      vadGate.onOpen  = (): void => transformer?.setVADOpen(true);
+      vadGate.onClose = (): void => transformer?.setVADOpen(false);
       vadGate.start().catch((e: unknown) => {
         this.logger.error("[VAD] failed to start", e);
       });