Two very similar TARDIS demats here.
This first one is a 3D fade out, look closely and you can see the back windows of the Police Box as it fades away.
(Quicktime, MPEG 4, 2.4 MB)
This one is more for reference, this is the classic dissolve trick, even if in the show it meant locking the camera in position for the shot.
(Quicktime, MPEG 4, 2.4 MB)
Why did you come here looking for insight?