OK - that's understandable. It works well and gives the desired result, but it is not "user friendly."
I realize that it is a difficult programming problem, so this suggestion may not be workable.
First the user would select the desired aspect ration (16x9, 4x3, etxc), then a "viewfinder" of the appropriate shape would appear over the image. The "i" key would zoom in, the "o" key would zoom out and the mouse would control where in the image the "viewfinder" would be. Press "record" ans start creating your Videomeld template for video file creation. In other words, it would be much like using a video camera viewfinder and adjusting the zoom to "crop" the scene as desired.
BTW - my video is now at:
https://vimeo.com/218067477