feat: noise gate implementation

src/livekit/NoiseGateTransformer.ts

@@ -0,0 +1,124 @@
+/*
+Copyright 2026 New Vector Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { type Track } from "livekit-client";
+import { logger } from "matrix-js-sdk/lib/logger";
+
+const log = logger.getChild("[NoiseGateTransformer]");
+
+export interface NoiseGateParams {
+  threshold: number; // dBFS — gate opens above this, closes below it
+  attackMs: number;
+  holdMs: number;
+  releaseMs: number;
+}
+
+/**
+ * Matches LiveKit's AudioProcessorOptions (experimental API, not publicly
+ * exported, so we declare it locally based on the type definitions).
+ */
+interface AudioProcessorOptions {
+  kind: Track.Kind.Audio;
+  track: MediaStreamTrack;
+  audioContext: AudioContext;
+  element?: HTMLMediaElement;
+}
+
+/**
+ * Matches LiveKit's TrackProcessor<Track.Kind.Audio> interface.
+ */
+export interface AudioTrackProcessor {
+  name: string;
+  processedTrack?: MediaStreamTrack;
+  init(opts: AudioProcessorOptions): Promise<void>;
+  restart(opts: AudioProcessorOptions): Promise<void>;
+  destroy(): Promise<void>;
+}
+
+/**
+ * LiveKit audio track processor that applies the OBS-style noise gate via
+ * AudioWorklet.
+ *
+ * Builds the audio graph: sourceNode → workletNode → destinationNode, then
+ * exposes destinationNode's track as processedTrack for LiveKit to swap into
+ * the WebRTC sender via sender.replaceTrack(processedTrack).
+ */
+export class NoiseGateTransformer implements AudioTrackProcessor {
+  public readonly name = "noise-gate";
+  public processedTrack?: MediaStreamTrack;
+
+  private workletNode?: AudioWorkletNode;
+  private sourceNode?: MediaStreamAudioSourceNode;
+  private destinationNode?: MediaStreamAudioDestinationNode;
+  private params: NoiseGateParams;
+
+  public constructor(params: NoiseGateParams) {
+    this.params = { ...params };
+  }
+
+  public async init(opts: AudioProcessorOptions): Promise<void> {
+    const { track, audioContext } = opts;
+
+    log.info("init() called, audioContext state:", audioContext.state, "params:", this.params);
+
+    const workletUrl = new URL(
+      "./NoiseGateProcessor.worklet.ts",
+      import.meta.url,
+    );
+    log.info("loading worklet from:", workletUrl.href);
+    await audioContext.audioWorklet.addModule(workletUrl);
+    log.info("worklet module loaded");
+
+    this.workletNode = new AudioWorkletNode(
+      audioContext,
+      "noise-gate-processor",
+    );
+    this.workletNode.port.onmessage = (e: MessageEvent<{ type: string; msg: string }>): void => {
+      if (e.data?.type === "log") log.debug(e.data.msg);
+    };
+    this.sendParams();
+
+    this.sourceNode = audioContext.createMediaStreamSource(
+      new MediaStream([track]),
+    );
+    this.destinationNode = audioContext.createMediaStreamDestination();
+
+    this.sourceNode.connect(this.workletNode);
+    this.workletNode.connect(this.destinationNode);
+
+    this.processedTrack = this.destinationNode.stream.getAudioTracks()[0];
+    log.info("graph wired, processedTrack:", this.processedTrack);
+  }
+
+  public async restart(opts: AudioProcessorOptions): Promise<void> {
+    await this.destroy();
+    await this.init(opts);
+  }
+
+  // eslint-disable-next-line @typescript-eslint/require-await
+  public async destroy(): Promise<void> {
+    this.sourceNode?.disconnect();
+    this.workletNode?.disconnect();
+    this.destinationNode?.disconnect();
+    this.sourceNode = undefined;
+    this.workletNode = undefined;
+    this.destinationNode = undefined;
+    this.processedTrack = undefined;
+  }
+
+  /** Push updated gate parameters to the running worklet. */
+  public updateParams(params: NoiseGateParams): void {
+    this.params = { ...params };
+    this.sendParams();
+  }
+
+  private sendParams(): void {
+    if (!this.workletNode) return;
+    log.debug("sendParams:", this.params);
+    this.workletNode.port.postMessage(this.params);
+  }
+}