Camera is 1920x1080 Video Action Cropping Left 400 Cropping Right 400 Corner Round 550 Camera is 1280x720 Video Action Cropping Left 300 Cropping Right 300 Corner Round 350 Adjust to taste.
The math as suggested by one user. Calculate what must be subtracted to get the same width & height. Divide that number by 2, remove it from both sides. "Round edges number" is the radius, which is the new box size. Scale as needed