According to the downloads section of replay it does have a build for 1.10 and development is still ongoing. I wonder how it stick an hour of video into 10mb. Does it not render it into actual video?
Using my magic powers of knowing roughly how everything works just by looking at it for 4 seconds, the way this would have to work is that it takes something like a snapshot of the world as it is when it starts, then saves all of the information the game would normally use to determine which blocks were updated and the location of the players, etc. That's all it'd have to save. Then the mod would reload the world and run the script back exactly as it happened the first time, only you'd have free reign with the camera and time.
Edit: I guess and easier way to put it, imagine like a fake server. This would record all the same stuff that would get sent over the 'net, then replay it all from whatever perspective you want.
And if that's not how they did it, it's how someone else who can do the coding should do it, because it would allow anyone on any single or multi player game to go back and record hours of whatever footage they wanted with the best possible quality at 60 FPS from any camera angle ever. Not to mention the idea that one could reasonably set it to record literally everything they've ever done in minecraft ever without any lag or crazy HDD requirements, with not only zero quality loss, but in fact dramatically improved quality regardless of PC specs.
But, the version they have doesn't work with most mods, and there isn't and never will be 1.7.10 support.