There is only one file type that uses the .KMV extension:
Mobile DJ Video File
Video file created on a Sansui mobile device, such as the H50T, using the bundled Mobile DJ app; saved in the Matroska video (.MKV) format, but uses an alternate file extension.
NOTE: If you are unable to open a KMV file, try changing the file extension to ".mkv" and open it with one of the media players below.
Updated: October 2, 2012