Conceptually, how does replay work in a game?

Question

I was kind of curious as to how replay might be implemented in a game.

Initially, I thought that there would be just a command list of every player/ai action that was t

Answer 1

I would believe that at certain increments the game would take a snapshot of the state of everything (EVERYTHING). Then when the replay is happening simple usage of linear-interpolation can be used to fill in the "holes". At least that is how i think it would be done.

You are correct that recording the inputs would be unreliable/not guarantee the same output. The game definitely has to keep track of the state of all the objects (or at least the important ones)