- Change XYZ Position of the layer to desired area. - Change XYZ Scale of the layer to desired area. - Change XYZ Viewpoint to show only desired area. - Apply a Global Mask and adjust the size. - Adjust the Edge Fade Shutters or, Framing Shutters Globally. - Apply an effect (either Globally or on the Layer) such as Pan+Scan (if the source image is larger than the native raster you are working with) or Edge Frame. - Create a custom 3D object to apply your video texture to.
What you want as your final outcome will determine what the best method is for any given situation.
The problem with adding imaging clipping on every layer is the number of channels that would require. Each layer would require an addition 8 channels of control for the image clipping, and with all nine layers it would be a total of 72 channels. The DL.3 is already at 481 channels, so adding 72 more would put it well over the 512 channel limit.
As Marty said, using scaling, positioning, or custom objects may help you achieve the look you are going for. Also, creating a custom JPEG to use as a mask is an option. Create a JPEG that is black and white, with black being the part of the image you want to crop (or the other way around, both will work), then layer that JPEG on top of a video and use the Chroma Key effect to make part of the mask transparent.