normalize audio

main.py

@@ -47,7 +47,9 @@ async def merge_audio(output_key: str):
     input_file = 'list.txt'
 
     try:
-        ffmpeg.input(input_file, format='concat', safe=0).output(output_file, c='copy').run()
+        intermediate_output = temp_dir + 'intermediate_output.mp3'
+        ffmpeg.input(input_file, format='concat', safe=0).output(intermediate_output, c='copy').run()
+        ffmpeg.input(intermediate_output).audio.filter('loudnorm').output(output_file, audio_bitrate='256k', ar='44100').run()
     except Exception as e:
         raise HTTPException(status_code=500, detail=f"FFmpeg Error: {e}")