As one zooms and edits, is there a way to just get something like a border guide around the screen area that will form part of the final export?  Only want it just as a guide to assist a zooming edit. Or perhaps change the black background screen area only to say white whilst editing and zooming so that I know if all this area is covered by my zoomed edit, then I will now have a full landscape image, or if not, how much of a border I will have either side?

For example, I have a 20 second (portrait) sequence of a dog running around a squelchy muddy field so am aware that one would automatically have black borders either side of the viewing area. I have spliced this sequence into quite a number of even shorter sections, and then zoomed in section by section in order to get reasonable close up’s as the dog roams around. Thought I had done quite a good job but on viewing the final export as MPEG4, I notice that one or two of my spliced sections are full landscape, but others I spot that the black borders at each side show and are of varying width. There is no constant and so is jarring on the eye.    

There is obviously a technique that I am missing. Any advice?

George