ReplayMod is great, I've made several trailers using it, and hope to make many more (Examples below).
Unfortunately, Spectator mode is not allowed in a lot of games, because it allows you to see what you want. If it was possible to make a replay format that has fly enabled when reviewing, but the player is not in spectator mode (meaning unable to travel through, or interact with blocks) or teleport to any player other than the player recording, there's a good chance that it'd be allowed on these games without losing too much functionality. This alternate version of ReplayMod, as I see it, could be pretty easy to make, but open it up to a new genre. I specifically want it for Mineplex's Clans, which currently does not allow ReplayMod.
We have something like this for about three years now. See here for details.
However, to this day it isn't fully implemented (i.e. any unknown restrictions sent by servers will prevent you from outright viewing the replay as a whole) because no big server seemed to be interested in using it.
To be clear: Servers can start using this right now to set restrictions on replays recorded in their games. At first this will prevent anyone from viewing such replays but once we update and implement the used restrictions, they'll retroactively work as expected. It's just that no big server seems to be interested.
So I can send this to my server, in theory, and they could implement this right now? Would this work completely server side? Because right now, the server just says it's not allowed, but has no way of preventing it, so this software would be welcome for them, if it was able to prevent illegal usage of ReplayMod, while also opening up a new way of legal usage.
Yes, they could implement this right now and it'll prevent any illegal usage of the RM. Legal usage will be prevented as well (just as it is right now) but only until the RM is updated to support the restrictions sent by the server.
Not sure what you mean by "completely server side". This works by the server sending a special packet to the client which the ReplayMod recognizes and treats appropriately.
To my knowledge the restrictions aren't bypassable, at least not by accident. Please ask them for more details. People can ofc just modify the RM to ignore the restrictions but then they might as well just install WorldDownloader.
"Legal usage will be prevented as well (just as it is right now) but only until the RM is updated to support the restrictions sent by the server."
By update, you mean an update you'd have to make once the server implements this, or an update that already exists that we'd need to download?
Also, how easy would it be for the server to detect if RM has been modified to, say, bypass these restrictions?
An update we have yet to make (we haven't yet because it'd be wasted time until some server uses the restrictions).
Detecting client modification on the server is impossible given a sufficiently smart modder (that applies to all software btw.). Even if we try to make it as hard as possible, at some point they might just as well write their own simple ReplayMod clone or just install WorldDownloader. As such we're not making our lifes any harder by trying to prevent such modifications.