I’ve just gone to do exactly the same thing, found your post and nothing more on it…
Frustrating, there should either be a dedicated field type in the metafields definitions or you should be able to specify a URL field type as being for video which restricts it to Vimeo & YT.
So frustrating as you port so much over to use dynamic references, but then you can’t for one thing so you’re left with a toe in the water…