I love this idea. If more box offices go with sending out electronic tickets instead of hard copies, that would be another way to use such a video.
I've said this for a long time. If people didn't grow up going to the theatre and their parents or whomever never taught them how to behave in the theatre and how it differs from other similar experiences like a sports game, a concert, or church, then how are we expecting people to know? Osmosis?