Deleting all Quicktime player MP-4 videos

When viewing my security camera videos I can open over 50 videos, and thumbnails. The thumbnails open in Preview, and one click will close all of the open thumbnails in Preview. However, I have to click each Quicktime video one at a time to close. Is there a way to close all of the open MP-4 videos with one click? It would sure save me a lot of time when viewing the SD card. Thanks