I was waiting until I saw something show up in my feed to verify and I just saw it.
Peertube is the fediverse version of youtube. Different peertube instances can connect together so people can view videos from all over the Internet from the one user interface.
I was running some testing figuring out what I could federate with, and I found that if I plug the URL from a peertube channel into my lemmy search, it shows up like a community. Then I can follow it and new videos will show up in my lemmy feed. (I expect the same would work in kbin)
So for example, the minetest videos channel is at https://share.tube/c/minetestvideos/videos – Just plug this URL into search, and suddenly minetestvideos is a community you’re following on lemmy or kbin, and new videos will show up in your feed and you can watch them and comment on them right from here!
It’s a really great example of how ActivityPub support lets you connect things you’d never expect to be able to connect. Imagine if on reddit you could just subscribe to a youtube channel!
Yes, they way activity pub works it will only pull over new content after the moment the instance you’re on becomes aware of the instance and community/user you’re pulling from.