Multiple viewers in sync? 1-5s, 500ms? *10*ms?

[Joshfindit]

This might be an question with an obvious answer, but over the whole pandemic I’ve been searching for video sharing services with one goal:

To get the viewers as in-sync as possible.

Vynchronize has been really decent, as has BigScreen on the Quest.
There have been dozens and dozens of potential solutions that have ended up in the nevermind pile just due to not getting this right (even Plex, which was stunning to me).

One of the bigger issues of course is how wildly latency can vary from server to client.
Linear video is uniquely suited to this since you can have a large buffer and just sync periodically (say, at key frames), but it also clearly requires specific thought and work around making that happen.

Functionality like:
-Watching video without echo while also being on a phone call together (or video chat on a separate device)
-Pausing the video to talk about it
-Rewinding to review (normally less than 60s)
-Rewinding to let someone catch up (they lost the video, or had something come up) (5-20 min normally, but could be arbitrarily anywhere in the video)

Are all things that come up across social usage scenarios like virtual classrooms, study sessions, movie watching, or even business presentations