Converting millisecond position in buffer~ to frame position in jit.buffer~

I have a question to which I'm sure there's an easy fix.

I would just like to specify a millisecond position in a buffer~ object and have it be converted it to a frame position in jit.buffer~ and for other Jitter objects.

I'm not playing any videos, just doing matrix operations, so there's no apparent "frames per second" value I can use for conversion...

Any help would be much appreciated!