There are two folders on DVD-Video discs: AUDIO_TS and VIDEO_TS - TS stands for "title set".
The AUDIO_TS folder is usually empty or not present on DVD-Video discs. If you wonder about the folder, you can go here
The VIDEO_TS folder contains .VOB, .IFO, and .BUP files. It stores all data for the DVD-Video. VIDEO_TS - Video Title Sets.
IFO files store control and playback information - e.g. information about chapters, subtitles and audio tracks. They do not store any video or audio data or subtitles.
BUP files are only backups of the IFO files.
VIDEO_TS.IFO file: the Video Manager (VMG) information file - stores control and playback information for the entire DVD - e.g. the First Play PGC (Program Chain), locations of all Video Title Sets (VTS), table of titles, number of volumes, domains for multiple languages and regional and parental control settings, information about subtitles, audio tracks, etc. This file is required to be present on a DVD-compliant disc.
VIDEO_TS.BUP file: the backup copy of the VIDEO_TS.IFO file. It is part of Video Manager (VMG).
VIDEO_TS.VOB file: the first-play Video Object of the DVD-Video disc, usually a copyright notice or a menu. It is part of Video Manager (VMG). This file is not required to be present on a DVD-compliant disc.
VTS_01_0.IFO file: stores control and playback information for the Video Title Set 01 - e.g. information about chapters, subtitles and audio tracks.
A "VTS_zz_0.IFO" file (where "zz" is from 01 to 99) is required to be present on each VTS.
VTS_01_0.BUP file: a backup copy of the VTS_01_0.IFO file. This file is required to be present on a DVD-compliant disc. It is part of Video Title Set (VTS).
VTS_01_0.VOB file: Video Title Set 01, Video Object 0, contains the menu for this title. This file is not required to be present on a DVD-compliant disc.
VTS_01_1.VOB file: Video Title Set 01, Video Object 1, contains the video for this title.
At least one file "VTS_zz_1.VOB" is required in the VTS and each "VTS_zz_x". DVD-Video can contain up to 99 (1-99) titles with max 10 (0-9) VOB files each. The last possible VOB file is VTS_99_9.VOB. ... etc.
On a movie DVD disc, movie video segments are stored as VOB files in the VIDEO_TS directory on the disc. So can we copy those VOB files to the hard disc and play them later?
The answer is no. This is because VOB files on most DVD discs are protected some anti-ripping encryptions.
Many movie DVD discs use Content Scramble System (CSS) encryption stop anyone rip off (copy) its contents from the DVD disc.
However, CSS encryption has been broken. There are many software on the Internet that implement De-CSS algorithm to rip off movie files of DVD discs.
Free DVD Decrypter is a freeware to help you backup DVDs to your computer.