diff --git a/robocyp.py b/robocyp.py
index 0836a42..70220da 100755
--- a/robocyp.py
+++ b/robocyp.py
@@ -17,7 +17,7 @@ _playlists = {}
 # output template: CHANNEL/DATE_TITLE_[ID].ext
 DEFAULT_OUTPUT_TMPL = "%(channel)s/%(upload_date)s_%(title)s_[%(id)s].%(ext)s"
 # download video 1080p or lower with audio
-DEFAULT_FORMAT = "bestvideo[height<=720]+bestaudio/best[height<=720]"
+DEFAULT_FORMAT = "bestvideo[height<=720][ext=mp4]+bestaudio/best[height<=720]"
 program_dir = os.path.dirname(os.path.realpath(__file__))