Another optional progress meter could be a digital/LED-style timer (either countdown or count up, user selectable) with two arrows underneat. Press and hold on a button and it moves in that direction. The longer you hold the faster it goes. Or do as some DVD players do: Press once for 2x, twice for 4x, thrice for 8x and so on.
I don't understand why there are two arrows? Do you have a picture of such slider? Can GST at all play at other then default speed?