The PIC can act as the divider chain. For example, in my CF player one display line is 617 instruction cycles. You'd have to modify that number for a different standard.
But don't get the idea that it's easy - I have coded many time-critical PIC applications where it is trying to do two or three things at once and so quickly that interrupts are useless (I rarely use interrupts!) The CF player is no exception. You go mad counting cycles
Anyway, I've tried that ffmpeg line and it produced a file of the expected size (well, 10msec over but I'll live with that). I'll get some of it into MATLAB and have a peek at it so that I fully understand the byte order etc.