When you explore the DVD drive, you will see at least two folders, an “AUDIO_TS” folder and a “VIDEO_TS” folder. AUDIO_TS is used for DVD audio and contains DVD-Audio files in the form of AOB. In a normal DVD, there is no file in AUDIO_TS. VIDEO_TS is used to store all the data for the movie and extras. There may be more folders which contain DVD-ROM features for your PC (e.g. software DVD player).
An example of DVD VIDEO_TS：
And you can see from the picture that DVD contains: VOB, IFO, BUP files.
VOB – Video OBjects, contains several streams multiplexed together: video, audio and subtitle. The video stream is encoded in MPEG-2. The audio on a DVD can be AC-3 (Dolby Digital), Linear PCM, and MPEG-2 audio (MP2). AC-3 is very much the standard. LPCM is mostly found on music DVDs and MP2 on cheaper productions.
A VOB can contain one main video stream and several multiangle streams, allowing you to switch the perspective during the movie. This feature is mostly used to display storyboards or other extra features during playback. The maximum bit rate of the video stream is 9.8mbit/s. Together, video and audio stream must be below 10mbit/s at any given moment. It’s possible to have up to 9 different audio streams and you can usually switch the audio stream during playback. It’s also possible to have up to 32 different subtitle streams. Subtitles are 4 color bitmaps which are overlayed over the video stream; they’re usually not encoded into the video stream.
IFO – InFOrmation
IFO Files give the player important navigational information, like where a chapter starts, where a certain audio or subtitle stream is located, etc. This is the reason why we can only rip DVD by chapters with a DVD ripper. IFO files are not encrypted.
BUP – BackUP
BUP files are just backup files of the IFOs (they are straight duplicates of them). Just like IFO files, they are not encrypted.