The DVD-Video and DVD-Audio specifications define how audio and video data are stored in specialized files. The .IFO files contain menus and other information about the video and audio. The .BUP files are backup copies of the .IFO files. The .VOB files (for DVD-Video) and .AOB files (for DVD-Audio) are MPEG-2 program streams with additional packets containing navigation and search information.
Since a .VOB file is just a specialized MPEG-2 file, most MPEG-2 decoders and software DVD players can play them. You may need to change the extension from .VOB to .MPG. However, any special features such as angles or branching will cause strange effects. The best way to play a .VOB file is to use a DVD player application to play the entire volume (or to open the VIDEO_TS.IFO file), since this will make sure all the DVD-Video features are used properly.
Many DVDs are encrypted, which means the .VOB files won’t play when copied to your hard drive. If you try to copy the .IFO and .VOB files to a recordable DVD it may not play.
.VRO files are created by DVD video recorders using the DVD-VR format. In some cases you can treat the files just like .VOB files, but in many cases they are fragmented and unplayable. Newer version of Cyberlink PowerDVD, InterVideo WinDVD, DVD X Player and Sonic Cineplayer can play them. Otherwise you’ll need a utility such as Heuris Extractor or Panasonic DVD-MovieAlbum to copy them to a hard disk in usable format. Alternatively you can use DVD disc creation software such as InterVideo WinDVD Creator, MedioStream neoDVD, or Sonic MyDVD can import from -VR discs and write out standard DVD-Video discs.