What are they:

Movie presets are files that can be created with WinDVD Tweakers Disc Manager to store certain movie configurations. They store the name of a General, Window, and Blanking preset that should be used with that certain movie. They also store the name of the Movie and the name on the DVD Disc. The files carry the file extension ".mve" and can be loaded from within WinDVD Tweaker or by double clicking them from outside WinDVD Tweaker.

See Disc Manager help here for more information on Movie Presets.

Extension:

.mve