This article shows you how to create full screen video.
You want to keep the file size low and keep all your scripts at the end of the html before the closing body tag if possible.
Use above the fold in page css to display the initial section quickly.
In the end you can’t preload something without it actually having to load. There will always be a time while something loads but you can show something else while this happens or indeed show nothing until the thing you want to see has loaded.
However a blank screen of even a few seconds is probably enough to make me think the site isn’t working and click somewhere else. I like to see things happen straight away even if they are only partially painted.