There is only one file type that uses the .NUV extension:
Video file created in the NuppelVideo format, which is commonly used by the MythTV free home entertainment software; often contains a video recorded from a video stream.
NUV files can be converted to .MKV, .AVI, or .MP4 files using mythnuv2mkv. VLC media player and MPlayer can play some NUV videos.
Updated: December 24, 2011