Just some quick observations:
1. Shouldn’t the range mapper’s input lower remain at zero and the input upper be set to frame rate? This way the expression follows the spline, instead of being a mirror reflection of it (0 remains 0 and 1 remains 1, instead of 0 becoming 1 and 1 becoming 0).
2. Also, is there an advantage to entering the frame rate value manually? Wouldn’t using the Time node’s Frame Rate make the expression more flexible?
Either way, I think I understood most of it, though I did need to watch it a couple of times to get everything.
All the best,
Jerome Olivier
PS
Hope I’m not being too exacting.