diff --git a/app.py b/app.py
index 703f435..bf3ff32 100644
--- a/app.py
+++ b/app.py
@@ -22,7 +22,7 @@ def run_download(job_id, url, format_choice, format_id):
     if format_choice == "audio":
         cmd += ["-x", "--audio-format", "mp3"]
     elif format_id:
-        cmd += ["-f", f"{format_id}+bestaudio/best", "--merge-output-format", "mp4"]
+        cmd += ["-f", f"{format_id}+bestaudio[ext=m4a]/bestaudio/best", "--merge-output-format", "mp4"]
     else:
         cmd += ["-f", "bestvideo+bestaudio/best", "--merge-output-format", "mp4"]