If you are looking for a YouTube alternative you have peertub. I suspect you are looking for a Plex alternative? That would be jellyfin. It's not federated, but it's FOSS.
People often conflate FOSS and Fediverse. Please correct me if I am wrong.
I believe this article is asking for a centralized media server for his multiple Fediverse deployments.
Say I post an image here on Lemmy, then jump on to Mastodon to toot it out to whatever followers I have there.
So that exact same image is stored twice.
I believe the ask is to build a system to store and deduplicate media posted across instances.