Need help to watch the replay!!!

Hi,

I just want to know how do u "rewind" or "forward" in the replay. I know its the sign "<<" for backward and ">>" for forward.

And also, it clearly stats in the replay which button to press to rewind or forward. But in most of the replay, its seems as I can't rewind or forward the replay and the "<<" or ">>" lookas as if its disabled. SO cant.

So, which button exactly for rewinding and forwarding the replay?
Any other information??

Thanks in advance