Not sure what I'm doing wrong or missing, but when I am key framing a digital zoom, normally the image simply goes from big to smaller as if the camera was zooming in. However, for some reason, the whole image seems to be getting smaller leading to black edges appearing the image. On some images, the zoom effect seems to be working correctly but then the black edges start appearing about halfway through. The edges occur even if the image is a full size image occupying the entire 1920 x 1080 frame.

Is there some setting I'm forgetting?

Any help appreciated.