Others have mentioned torrents, which is worth investigating for ordinary video files.

Another option is vector animations (a la Flash). I'm not saying we should revive Flash (may it remain dead). On the contrary, a new vector animation markup language is needed. SVG can do some of what is needed, but SVG requires Javascript to do more than trivial animations, especially for interactivity. And adding a scripting language to a Nostr NIP would be a very bad idea, because the security of scripting engines is generally poor; Chrome and Firefox just barely manage to keep Javascript in random websites from getting at your passwords.

I have a design for a markup language that would do what is needed (animations, sound, interactivity without scripts). And what's more, it is generic enough to be used as a replacement for HTML too. For that language to go anywhere, I would need someone to work with, since I don't have time to do the coding.