Shinsuke Matsumoto (@Beatgram) has posted a concise explanation of the After Effects loopOut expression. If you are unfamiliar, the loopOut expression in Ae, will allow you to easily loop any part of your layer using the keyframes that you have already set.
We have seen many, many tutorials that will take you through the ins-and-outs of using the loopOut expression, and all of its ancillary elements.
The difference here is how easily you can gleam all you need to know about how to use the loopOut expression in a simple 4 frame animated GIF.
As Shinsuke Matsumoto notes in the article, loopOut has 2 arguments which correspond to a loop type and the number of keyframes to loop. It is in the number of keyframes that you can control which segments of the last keyframes to loop.
Its counterpart loopIn, does the exact same effect, only starting with the first of animated keyframes instead of loopOut’s counting from the last. Check out Beatgram’s post for looping animations with After Effects using the loopOut Expression.
More Resources for Using the LoopOut Expression in Ae
You can start with a detailed look at loopOut, with Matthew Tompkins covering all the uses of the loop expression in After Effects. Showing loopOut(), loopIn(), loopInDuration(), loopOutDuration() commands and their “ping pong”, “cycle” and “continue” modes – check out the article for Using the Loop Expression in After Effects.
David Torno expands on looping in Ae with Using Loop Expressions in After Effects for Video & Properties, showing how you can use its functions on video, but also animated properties as well.
Shawn Sheehan offers a practical example for using looping in Ae showing how to loop a simple run cycle animation over the length of the composition, with the post Looping After Effects Animations using Expressions.
Another practical example is a tutorial from Evan Abrams, where he shows how to create an animation of infinite opening doors in After Effects making it possible with the loopOut Expression – Creating an Infinite Door Animation Making Use of the Loop Expression.