Remove await from audio worklet

Co-authored-by: Fedor Indutny <79877362+indutny-signal@users.noreply.github.com>

.oxlint/rules/enforceFileSuffix.mjs

@@ -209,6 +209,7 @@ const STD_PACKAGES = new Set([
   '@react-types/shared',
   '@signalapp/minimask',
   '@signalapp/quill-cjs',
+  '@signalapp/lame',
   '@typescript-eslint/eslint-plugin',
   '@typescript-eslint/parser',
   'axe-core',

packages/lame/README.md

@@ -22,8 +22,9 @@ cd -
 emcc -I lame-3.100/include -Oz -DNDEBUG -flto wrapper.c \
     ./lame-3.100/libmp3lame/.libs/libmp3lame.a -o wrapper.mjs \
     -sEXPORTED_FUNCTIONS=_wrapper_init,_wrapper_get_num_samples,_wrapper_get_in,_wrapper_get_out,_wrapper_encode,_wrapper_flush,_wrapper_get_lametag_frame,_wrapper_close \
-    -sEXPORTED_RUNTIME_METHODS=HEAPU8 \
+    -sEXPORTED_RUNTIME_METHODS=HEAPU8 -sDYNAMIC_EXECUTION=0 \
     -sENVIRONMENT=worklet -sWASM=0 -sWASM_ASYNC_COMPILATION=0
+sed -I '' 's/^async //' wrapper.mjs
 ```
 
 ## License

packages/lame/index.mjs

@@ -12,7 +12,7 @@ const {
   _wrapper_encode,
   _wrapper_get_lametag_frame,
   _wrapper_flush,
-} = await initWrapper();
+} = initWrapper();
 
 const input = new Float32Array(
   HEAPU8.buffer,

ts/services/audioRecorder.dom.ts

@@ -77,10 +77,15 @@ export class AudioRecorder {
       }
       if (data.type === 'complete') {
         this.#state = { type: 'idle' };
+        chunks.push(data.finalFrame);
+
+        const result = Bytes.concatenate(chunks);
+
         // Replace the original placeholder header with the one that has
         // full audio duration (necessary for VBR encoding).
-        chunks[0] = data.lametagFrame;
-        resolve(Bytes.concatenate(chunks));
+        result.set(data.lametagFrame);
+
+        resolve(result);
         return;
       }
     };
@@ -88,7 +93,6 @@ export class AudioRecorder {
     const stream = await navigator.mediaDevices.getUserMedia({
       audio: {
         channelCount: { ideal: 1 },
-        autoGainControl: { ideal: false },
       },
     });
 

ts/types/AudioRecorder.std.ts

@@ -21,6 +21,7 @@ export type WorkletMessageType = Readonly<
   | {
       type: 'complete';
       lametagFrame: Uint8Array<ArrayBuffer>;
+      finalFrame: Uint8Array<ArrayBuffer>;
     }
 >;
 

ts/workers/mp3Encoder.std.ts

@@ -5,6 +5,7 @@ import type {
   WorkletMessageType,
   RendererMessageType,
 } from '../types/AudioRecorder.std.ts';
+import { init, encode, flush, getLametagFrame } from '@signalapp/lame';
 
 declare const sampleRate: number;
 
@@ -33,16 +34,7 @@ declare function registerProcessor(
 
 const BIT_RATE = 128;
 
-// Unfortunately `context.audioWorklet.addModule` doesn't wait for top-level
-// awaits to be resolved so we have to call `registerProcessor` immediately
-// and let the import resolve later on.
-const lame = (async () => {
-  const result = await import('@signalapp/lame');
-
-  result.init(sampleRate, BIT_RATE);
-
-  return result;
-})();
+init(sampleRate, BIT_RATE);
 
 class Mp3Encoder
   extends AudioWorkletProcessor
@@ -53,21 +45,22 @@ class Mp3Encoder
   constructor() {
     super();
 
-    this.port.onmessage = async ({ data }: { data: RendererMessageType }) => {
+    this.port.onmessage = ({ data }: { data: RendererMessageType }) => {
       if (data.type !== 'stop') {
         throw new Error('Unexpected message');
       }
       this.#isStopped = true;
-      const { flush, getLametagFrame } = await lame;
-      this.#sendChunk(flush());
+
+      const chunk = new Uint8Array(flush());
 
       const lametagFrame = new Uint8Array(getLametagFrame());
       this.port.postMessage(
         {
           type: 'complete',
           lametagFrame: lametagFrame,
+          finalFrame: chunk,
         } satisfies WorkletMessageType,
-        [lametagFrame.buffer]
+        [lametagFrame.buffer, chunk.buffer]
       );
     };
   }
@@ -83,19 +76,16 @@ class Mp3Encoder
     }
 
     const [channel] = input;
-    if (channel != null) {
-      void this.#encode(channel);
+    if (channel == null) {
+      return true;
     }
-    return true;
-  }
 
-  async #encode(channel: Float32Array<ArrayBuffer>): Promise<void> {
-    const { encode } = await lame;
-    this.#sendChunk(encode(channel));
-  }
+    const shared = encode(channel);
+    if (shared.length === 0) {
+      return true;
+    }
 
-  #sendChunk(chunk: Uint8Array<ArrayBuffer>): void {
-    const copy = new Uint8Array(chunk);
+    const copy = new Uint8Array(shared);
     this.port.postMessage(
       {
         type: 'chunk',
@@ -103,6 +93,7 @@ class Mp3Encoder
       } satisfies WorkletMessageType,
       [copy.buffer]
     );
+    return true;
   }
 }