Hi Gary;
It doesn't even have to support playback... Or at least, not to a DAC. On-screen preview is fine. Might be nice to have a speed slider though.
But yeah, my vision is similar to yours. Basically a file browser... Load a bunch of frames, select the ones you want, preview them if you want to, and then save the selected frame(s) to a separate file. Pretty basic stuff... (You can probably re-use large sections of code from Spaghetti!)
Adam