The ‘Pan Behind’ Tool in Adobe After Effects
Keyframing content beneath a mask to create a magnify effect

This is a somewhat obscure technique for Adobe After Effects, not because it’s particularly difficult, but because it rarely comes up. Nevertheless, it’s a handy one to know should the need arise. You have a mask on a layer, and you need to animate the layer’s content while leaving the mask fixed in place. How do you do it? We’ll walk through a simple project to see how it works.
 
The key to this process is simply knowing which tool to use and which parameters to keyframe. The tool is the Pan Behind tool; and the parameters to keyframe are the Mask Shape and the layer’s Position. And here’s how it works.