Have you ever wondered how the files work on a DVD? To break it down, let’s first take a look at the file system used on a DVD disc. Generally, there are two folders on a DVD: VIDEO_TS and AUDIO_TS. Usually the AUDIO_TS folder is empty. However, the VIDEO_TS folder contains three types of files: the .VOB files, .IFO files and .BUP files.
How do these files work?
.VOB (video object) files are used to save all the video and audio data in MPEG-1 or MPEG-2 format. That data contains the video content, Menu, buttons and sub-picture streams that control multiple audio tracks and subtitles.
.IFO (information) files are used to control the playback of .VOB files. This is where you can find the controlling information about when and how to play the .VOB files, for example, the chapters and menu navigation.
The .BUP (backup) file is a backup of the .IFO file. The .IFO files are very important to the normal playback of the DVD video, so it needs a backup in case any unlucky situations happen.
If the .IFO and .BUP files are missing, most video players will not be able to play the .VOB files.
So now we understand the three types of the files on DVD discs: IFO-VOB-BUP.
Naming Conventions and Size
The .VOB files in VIDEO_TS folder are usually named using the following format: VTS_xx_y.VOB. Here the “xx” is the program number, a number from 01 to 99. “y” can be numbered from 0 to 9.
Each file in a MicroUDF (Universal Disk Format) file system can only hold a maximum of 1 GB of video content, so many movies have to be stored in several VOB files.
Three Types of Data
A DVD disc includes three types of media data: video, audio and sub-picture. DVD videos usually adopt the MPEG-2 compression algorithm and DVD video streams can support Multi-Angle movies. A Multi-Angle movie is shot by several cameras from several angles (9 angles maximally) at the same time. This Multi-Angle function allows the viewer to choose any one angle he likes the most.
DVD videos also support Line 21 Closed Caption. For audio streams, a DVD can have maximally 8 audio streams within it (8 audio streams mean 8 dubs of different languages). A DVD can be compatible with various audio formats like AC3, MPEG, LPCM, DTS, SDDS, etc.
A subpicture is a graphical display system which is a part of DVD-Video. It is mostly used to display subtitles, but it also can be used for menu highlighting and some other effects. A DVD can have, at most, 32 subpicture streams.
Titles, Chapters, and Menus
The most important logical category on a DVD is called Title. One DVD disc can have 99 titles maximally. One title usually means one whole movie or a part of a video program.
Each title can be comprised of 999 chapters at most. Chapters are designed to provide user convenience for visiting any point of the video. After playing one chapter, the next chapter can be automatically played or the user can go back to the Menu interface.
The communication between the users and DVD depends on the Menus. There are two types of menus: Video Manager Menu (VMGM, also called the Top Menu or Title Menu) and Video Title Set Menu (VTSM, also called the Root Menu, although it is not the real “root” menu). VMGM allows users to go to the main titles or title collection. If you choose a title, the VTSM submenu will show. The VTSM menu contains buttons that will let you access each title. It also includes the audio track, angles, subtitles, chapters and other submenus. The VTSM menu is an optional choice for users. Users need not enter it if they prefer not to.
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