Background mp4 sometimes too small

Some times when using an mp4 as a background it does not fill the screen, making it obvious the that scene behind is just a video because my portrait extends past the bottom of the video playing in the background. When this happens it applies to all the mp4’s but not the jpg backgrounds, and when it works correctly it works correctly for all the mp4’s. So it is not the mp4 itself. Is there any fix for it?

Was able to see this issue once using a Brio 4K but unsuccessful to repeat the issue.
May we know the webcam you are using? This might be a conflict with the resolution used by the camera.