Accordying to my calculations, this should be working, but for some reason the shift between frames falls out of phase after a few seconds, and I cant figure out why. (you can see it working for a little bit then it wonks out)
Can any of you quickly see what is wrong?! or am I misunderstanding how the speed node in the flipbook works?
Video of how the shader (not)working - https://imgur.com/0akIWnL (you can see it in the correct phase for a little bit in the middle of the video.

Essentially I am trying to make a super simplified version of this: http://www.klemenlozar.com/frame-blending-with-motion-vectors/
Thanks!