diff --git a/ar_tag_pose/detector_board_main.py b/ar_tag_pose/detector_board_main.py
index 56507ec..07bc3bb 100644
--- a/ar_tag_pose/detector_board_main.py
+++ b/ar_tag_pose/detector_board_main.py
@@ -231,7 +231,7 @@ def main():
 
 	out_file = None
 	if args["output"]:
-		out_file = args["name"]
+		out_file = f"{args["name"]}.mp4"
 
 	detector = Detector(args["source"], board_detector, out_file=out_file)
 	detector.board_image_generate(margin_length=args["margin_length"])