I have three layers of stills that I want to use to produce a moving image; the back layer is a starfield, the mid-layer is a debris field and the front layer is a driver in a vehicle. You can see through the window - I made the window white, set Chroma key to white and the background for the debris is white, and then I set the mid-layer to pan right to left.
That all works fine; the debris 'flies' between the vehicle and the background stars - BUT even though all images have been sized to 720 width, when I export the movie there is a vertical band on each side of the forground image, and it shows the moving debris field on each side of the front image, beyond the normal borders. WHY does that happen and how can I control the image so that it does not appear outside the 720 horizontal width limit that is the actual size of my images and the selected output size; only 720 - why is it wider?