Film and television are shot in front of the mirror, why can't we see the camera and the staff?

If the mirror is not completely front, the close-up of the horizontal angle can be appropriately adjusted by the angle of light reflection. Or the effect of two films superimposed together in post-production. Usually the background film is transparent, and only the outline of the object can be seen; The physical film is diluted and shallower than the normal lens film. These two add up to a "look in the mirror" picture. If you can't see it in front of the mirror, it is that the software was disposed of in the later stage of the film and television.