Putting each segment into it's own NOSTR event makes a lot of sense for live streaming but for videos that would be an unnecessary overhead. There is also a chunked blobs BUD10 draft

GitHub

blossom/buds/10.md at chunked-blobs · hzrd149/blossom

Blobs stored simply on mediaservers. Contribute to hzrd149/blossom development by creating an account on GitHub.

but that is more for generic files with fixed blob sizes.