He doesn't mean a scroll bar, like the thing on the right of this page. He means a bar like youtube videos have, so he can skip or rewind to a certain time.
Yeah, I know what he meant, I just didn't pick the right word.
Most RTS replays work by just shoving back in the mouseandkey events processed during the game at the right times and letting the simulation run accordingly. It's hard to "fast-forward" or "skip through" something like that, as it's not a video, it's actually being calculated real-time as you are watching it.