First of all, it is feasible to add a black box, which can be realized by ordinary computers with audio and video or Vegas. If the resolution difference between materials is large, it will cause different sizes, which will greatly affect the consistency of the picture.

I personally don't recommend this method. I suggest to unify the materials with different resolutions through masking, which can greatly reduce the sense of disobedience, but some edge parts of the picture may be abandoned, and the materials with smaller resolutions may also appear mosaic. The mask function in vegas is relatively simple to use. If it is a computer with MAC system, it can also be realized by software such as FCP(Final Cut Pro).

I hope it helps you.