File Extension BUP
File extension BUP is used by backup files on DVD Video disks. These files contain the same data as File extension IFO files: subtitles, tracks, menus, chapters. DVD players fall back to reading data from these files in situations when IFO files are unreadable. Most common cause for this are scratches and other "tear and wear" of the optical media.
While BUP files can not be directly opened by any program disks containing these files can be played using DVD playback software such as Windows Media Center, PowerLink DVD Player etc. These files can also be created by DVD authoring software.