What is BUP file?

File extension bup is commonly backup of DVD ifo file.

The .BUP file extension is used by a variety of software as a backup of the IFO file found on DVDs. The IFO file stores various information, on the DVD, such as tracks or subtitles, and the backup is useful in case the primary VIDEO_TS.IFO file is unavailable or corrupted (due to a scratch on the surface of the disc). BUP files should be accessed by a media player and it shouldn't be necessary to open then directly yourself.

Like IFO files, BUP files are not encrypted.