DVD Copying - The basics [1/2]: "What’s on a DVD?
If you have purchased a DVD that you want to copy, you can put it in your DVD-ROM drive to check out its contents. On the disc you will find several folders with files in it. Normally you should always see a VIDEO_TS and AUDIO_TS folder. The AUDIO_TS folder is used to store DVD Audio, the VIDEO_TS to store DVD Movies.
We will be focusing on a movie DVD, so we’ll enter the VIDEO_TS folder. In this folder you will find .VOB .BUP and .IFO files. The VOB file contains the actual movie files. This is a MPEG-2 encoded file. Simplfied is MPEG-2 is a method of compression for movies, just like MP3 files are compress audio. The file contains also audio, normally this should also be a compressed format. Mainly it is an improved form of MP3, named AC-3. Besides that contain the .VOB files the subtitles and multiple camera angles.
The .IFO files are the information files, used by your DVD playing device. It gives the DVD player information on what .VOB files to load and when. E.g. when to start a new chapter. The .BUP files are simply a backup of the IFO files and generally have no use, they will only be used when an .IFO files become unreadable somehow."