The only legal vertical resolutions for DVD video are 480 and 240 for NTSC or 576 and 288 for PAL. Standards compliant Horizontal resolutions are 720, 704, and 352 for either system, but many standalones will playback video with a horizontal resolution of 480. In any case, if you want to change the resolution you'll need to re-encode the MPEG-2 video stream.