It’s not going to be easy to do as you would require a field to add the embed code (assuming you’re using embed) and in theory that would enable anything to be added. You could check that field for some ‘similar’ code like youtube or vimeo tag perhaps.
Perhaps you could take a more ‘design’ approach and style so it makes sense to only upload video. You’d then at least be making it clear this is what the field is. Wording would help there also and you can add custom strings of text or even modify the existing text using a mo/po file.
Others may have some ideas though that’s just my first thoughts.
Is it not possible to add some code to check whether a post is a link or not? And a way to find out if the string contains the text “youtube.com” or “vimeo.com”? And then throw an error message if it doesn’t?
That was my only idea so far…
so i think you can already sort of do what you are trying to do with just the activity feeds i’m not sure if it requires jetpack or not but whenever someone makes an activity update with a youtube url in it the system should automatically embed the youtube video. i don’t think it works with vimeo though.