Have some film grain or an overlay that only lasts for 20 seconds? Well, here is a very simple method on how to loop that clip in Adobe After Effects CS6.
1). In the main project window, right-click the file that needs looping.
3.) In the pop-up window at the very bottom there is a looping option. Enter the amount of times you want to loop the footage. Input a high number for ease.
You can now expand the clip or effect to your hearts desire.