add opening sound FX

.gitattributes

@@ -32,4 +32,5 @@ saved_model/**/* filter=lfs diff=lfs merge=lfs -text
 *.xz filter=lfs diff=lfs merge=lfs -text
 *.zip filter=lfs diff=lfs merge=lfs -text
 *.zst filter=lfs diff=lfs merge=lfs -text
+*.wav filter=lfs diff=lfs merge=lfs -text
 *tfevents* filter=lfs diff=lfs merge=lfs -text

front/src/components/PodcastGenerator.tsx

@@ -8,6 +8,7 @@ import {
   loadWavAndDecode,
   pickRand,
 } from '../utils/utils';
+import openingSoundSrc from '../opening-sound.wav';
 
 interface GenerationStep {
   turn: PodcastTurn;
@@ -130,6 +131,8 @@ export const PodcastGenerator = ({
         step.audioBuffer = await loadWavAndDecode(url);
         if (i === 0) {
           outputWav = step.audioBuffer;
+          const openingSound = await loadWavAndDecode(openingSoundSrc);
+          outputWav = joinAudio(openingSound, outputWav!, -1);
         } else {
           const lastStep = steps[i - 1];
           outputWav = joinAudio(

front/src/utils/utils.ts

@@ -219,7 +219,24 @@ export const loadWavAndDecode = async (url: string): Promise<AudioBuffer> => {
     throw new Error('AudioContext is not supported on this browser');
   }
   const audioCtx = new AudioContext();
-  const audioBuffer = await audioCtx.decodeAudioData(arrayBuffer);
+  let audioBuffer = await audioCtx.decodeAudioData(arrayBuffer);
+  // force mono
+  if (audioBuffer.numberOfChannels > 1) {
+    const monoBuffer = new AudioContext().createBuffer(
+      1,
+      audioBuffer.length,
+      audioBuffer.sampleRate
+    );
+    const monoData = monoBuffer.getChannelData(0);
+    for (let i = 0; i < audioBuffer.length; i++) {
+      let sum = 0;
+      for (let channel = 0; channel < audioBuffer.numberOfChannels; channel++) {
+        sum += audioBuffer.getChannelData(channel)[i];
+      }
+      monoData[i] = sum / audioBuffer.numberOfChannels;
+    }
+    audioBuffer = monoBuffer;
+  }
   return audioBuffer;
 };