typo

app.py

@@ -61,7 +61,7 @@ def download_video(url):
     # by default select 480p and .mp4 
     format, format_id, fps = select_video_format(url)
     if format_id is not None:
-        dl_opts = {
+        ydl_opts = {
         'format':format_id,
         'outtmpl': "videos/%(id)s.%(ext)s"}