As the name says MPV Decoder will help to decode MPV files.
MPV is a MPEG-1 or MPEG-2 video elemantary stream (no audio). Also called M1V for MPEG-1 video and M2V for MPEG-2 video.
Sometimes you can just rename the files .mpg and play them in Windows Media Player or other DirectShow player. However, if you get errors about not being able to play them, install MPV Decoder.