It is possible with Corel (Ulead) Video Studio ProX2 to change the basic dimensions of a mask (aka a garbage matte) in that you can control the mask's overall height and width.
But it seems you cannot change, when changing width, for example , only the location of the right border; you must change both the right and left borders at the same time.
And once you have set the dimensions, you cannot move the mask to a desired area in your frame. Instead, the center of the mask seems "locked" to the center of the screen.
The result is that the only way to make an adjustable mask which includes the subject and only the subject, is to have a subject which is centered in the screen; a subject standing off to the right, for example, cannot be isolated.
Does anyone know a way around this?