diff --git a/api/app.py b/api/app.py
index 2f7e246..3167461 100644
--- a/api/app.py
+++ b/api/app.py
@@ -155,7 +155,8 @@ def download():
 
         if mode == "video":
             if format_id:
-                ydl_opts["format"] = format_id
+                # Use specific format ID + best audio, then merge
+                ydl_opts["format"] = f"{format_id}+bestaudio/best"
             else:
                 ydl_opts["format"] = "bestvideo*+bestaudio/best"
         else: