diff --git a/ar_tag_pose/detector_board_main.py b/ar_tag_pose/detector_board_main.py
index 8dce1b4..ba185f5 100644
--- a/ar_tag_pose/detector_board_main.py
+++ b/ar_tag_pose/detector_board_main.py
@@ -166,7 +166,7 @@ class Detector(abc.ABC):
 		cv.destroyAllWindows()
 
 def out_writer(writer: cv.VideoWriter|None, frame: np.ndarray|None, filename: str = None) -> cv.VideoWriter:
-	if writer is None:
+	if writer is None and filename is not None:
 		fourcc = cv.VideoWriter.fourcc(*"mp4v")
 		frame_size = (frame.shape[1], frame.shape[0])
 		writer = cv.VideoWriter(filename=f"{RESULTS_FOLDER}/{filename}", fourcc=fourcc, fps=30.0, frameSize=frame_size)