Rather than adding video files to your default results, which clutters results when you want to do simple things like launch apps, try using the "open" keyword (or pressing the spacebar, which is a shortcut for it)
For example "[spacebar]rolling" brings up relevant .mov and .avi videos on my Mac.
If you're new to Alfred, take a look at this guide to searching using Alfred, which shows you the difference between searching for apps and for general files:
https://www.alfredapp.com/blog/tips-and-tricks/beginners-guide-to-alfred-searching-your-mac-and-the-web/
