You're animating to a music track in After Effects and need to loop keyframes or footage. But after just a few bars the keyframes start to stray off-beat.

Did you get the BPM wrong? Maybe. But this will happen even if you're spot on.

Why?

AE rounds the loop point to a full frame time. So the only way it can remain perfectly on beat is if the BPM is a perfect multiple of the frame rate [30fps / 120bpm].

This simple expression will accurately loop based on the bpm that you enter, and the number of beats you want to include in the loop. Give it a try, and let me know if you find it helpful.