This is a clever video effect. You pick output pixels from different input frames depending on the y coordinate. The end result is very smooth, which explains the author’s mention of “60 fps -> 512×512”, which implies a time slip of about 9 seconds top to bottom if it’s one frame per pixel.
Originally shared by Alex Fink
Here’s what the shear (x’, y’, t’) = (x, y, t – y) looks like.