ok if you update lay theme now, go to customize → intro.
here u will find:
Screenshot 2025-01-24 at 18.25.08.png
in here, you can add the html code of your video
you'd need to write custom css for that video to be sized properly and for it to have the correct placement inside the intro
if you want i can help you with this but first u'd need to add your html there and then post the link to the website
about having a video background for the website:
you'd need to add your video html markup in:
lay options → custom css & html → custom html at bottom
then you'd need to write css to position that video correctly
i can also help u with that, but first you'd need to add the html there and then post a link to your website here