If you are interested in setting up your dynamic layers to accommodate both portrait and landscape footage (photos or videos) within a composition, here’s how to do that:
We will assume that you are creating a “square” precomp, and that you want the footage to fill the composition in either direction and to letterbox or pillarbox that footage appropriately.
First, the most important thing is that rather than having the composition be a perfect square, you need to make sure that your width is at least 1px longer than the height. So rather than 800 px x 800 px, it would need to be at a minimum 801 px x 800 px. This is going to be true even if you aren’t going for a square precomp. The letterbox/pillarbox will not work if the comp is taller than it is wide.
Add the Templater Settings effect to your desired footage layer. In the Templater Settings effect, in the “Layout” section, you have the option to set a “Scale factor”- you’ll want to set that to 100%. In the “Alignment” section there is an option “initialize to center”- make sure to enable that.
That should be all you need to accommodate footage sources of different dimensions.