The Resize node changes a clip's resolution, frame depth, and aspect ratio. You can then select and animate the portion of the source clip that appears as the destination clip to create the result image.

See Resize Settings.

You can add a Resize node to any part of the pipeline except to the blend node pipes. Typically, you would add it to the branch for the back clip, since the resolution of the front and matte clip are usually the same.

You can input a back clip with a different resolution from the front and matte clip to the Modular Keyer node in Batch. However, when you enter the Modular Keyer editor, the Result node does not process a full composite for mixed resolution input. Add a Resize node to change the destination resolution so all input has the same resolution. See Modular Keyer Node.