+/** 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
+
+ 1/f = Fd/f
+ ie 1 = Fd
+ ie d = 1/F
+
+ So for a 3hr film, ie F = 3 * 60 * 60 = 10800, the acceptable
+ FPS error is 1/F ~= 0.0001 ~= 1e-4
+*/
+#define VIDEO_FRAME_RATE_EPSILON (1e-4)
+