-static bool
-about_equal (double a, double b)
-{
- /* A film of F seconds at f FPS will be Ff frames;
- Consider some delta FPS d, so if we run the same
- film at (f + d) FPS it will last F(f + d) seconds.
-
- Hence the difference in length over the length of the film will
- be F(f + d) - Ff frames
- = Ff + Fd - Ff frames
- = Fd frames
- = Fd/f seconds
-
- So if we accept a difference of 1 frame, ie 1/f seconds, we can
- say that