In Delight you can decide a general background for the entire site, but also a different background in any page (this option overwrites the previous, of course).
In this case you can see a video as background. It is very simple to set.
If you want that all your pages have a video as background (self hosted video, FLV format), just set the default background in the Delight Admin Panel:
If you want to apply a particular video to one page only, a custom box in the page itself allows it: