Update app.py

app.py

@@ -551,7 +551,7 @@ async def run_tts_pipeline(task_id: str, story: StoryCreationDTO):
         print(f" final_generated_story_path: {final_generated_story_path}")
 
         wav = AudioSegment.from_wav(final_generated_story_path)
-        mp3_path = final_generated_story_path.replace(".wav", ".mp3")
+        mp3_path = final_generated_story_path.with_suffix(".mp3")
         wav.export(mp3_path, format="mp3", bitrate="192k")
 
         print(f" final_generated_story_path after conversion to mp3: {mp3_path}")