Looping a Composition - After Effects

This will loop your entire composition.

1. Set your work area to the part of the composition you wish to loop and from the menu bar select Composition -> Trim to Work Area.
2. Create a new composition, Shift Command K, and place the composition you wish to loop into your new composition. If you precompose, and effects will stay on the master composition and won't be looped. This can cause problems if you are rotobrushing for example.
3. In your new composition, go to the menu bar select Layer -> Time ->Time Remapping.
4. Time Remapping will create two key frames, one at the beginning of your composition and one at the end. Move to the very last key frame, step backwards one frame and create a new keyframe.
5. On the very last keyframe change the time to 0.
6. Select the Time Remapping effect from the layer's panel and from the menu bar select Animation -> Add Expression.
7. Time Remapping will now have an expressions box. Click on the Expressions Language menu icon, it will look like this File:Expression icon.jpg, and Property -> LoopOut(Type="Cycle", numKeyframes = 0)
8. Now you may extend the looping composition and it will loop repeatably.