VOB (Versioned Object Base) is a container file format that can comprise different data types. All films and music videos recorded on DVD discs are stored in these files; they contain several audio and video streams as well as subtitles and film or music video menu.
DVD discs unlike CD ones have greater data density, two-layer recording and better protection. The date of first mention of DVDs is believed to be 1994, when a special board in Hollywood set requirements that all motion pictures recorded on compact discs were to follow. A consortium called in 1995 that included Philips, Pioneer, Hitachi, JVC, Matsushita, Mitsubishi, Sony and other companies meeting the board requirements presented a brand new disc record format –MMCD (Multimedia CD); Toshiba and Warner presented format SD (Super Disc). At the same time a general agreement was approved, to find a uniform standard that was called DVD. MPEG-2 was chosen as a video encoding format. A year later, in 1996, Japan brought to market first DVD players and in 1997 sales started in the USA. Europe got DVD players and adapted discs in 1998.
If you look at the content of any DVD disc on a computer, you’ll see that it consists of at least two folders and a long list of files. One of the folders, AUDIO_TS, has audio tracks that are used mostly on audio DVD discs. The second one, VIDEO_TS, contains a large number of files the film consists of and navigation information. There are three types of files in VIDEO_TS folder. These are VOB (video object) with audio and video information, IFO (information) with navigation information and configuration, and BUP files, which are back-up copies of IFO files on outer tracks of DVD discs and meant for use in case of damage of IFO files.
Base units of DVD disc file system are VOB files. They can contain video tracks, subtitles used in the given VTS set with all soundtracks, image versions with text for other languages, alternative camera angles – all that is stored in one file of this type.
Video in VOB files is saved in MPEG2 format with definition of 720 x 480 for NTSC disc, and with definition of 720 x 576 for PAL files. VOB files can be used to record the main content of the chapter. Moreover, VOB files can be in the chapter menu, if this menu has opening videos in addition to static images.
When dealing with VOB files a player not only plays their audio and video content, but also follows the instructions in them that display the menu, or the menu selections chosen by a program user. VOB files can’t be bigger than 1Gb, that’s why the folder can contain several of them. When a DVD has a lot of information, there will be more than one VTS set with VOB files inside.
Every VOB file consists of special cells that are the smallest DVD units the user is redirected to at interactive watching. These cells comprise of a certain number of image groups called MPEG GOP. All cells are connected by navigation program chains (PGC) that determine their playback order depending on the chosen program. The sequence of interconnected scene playback is set in advance by a corresponding chain. Every chapter can have just one chain called One_Sequental_PGC_Title, or several chains Multi_PGC_Title. A number of cells may be simultaneously engaged in more than one chain, a user gets in other cells only in particular cases.
Recording of DVD discs is like the same operation with other disc types. They can be recorded with the help of Nero Express program which not only records movies and videos having DVD format, but also makes it possible to convert ordinary video CDs into the format that enables DVD replicating. You can use free program CDBurnerXP with a multi-language interface. This program also allows to create and record ISO images. Ashampoo Burning Studio is quite popular as well and helps you record DVD-R, DVD-RW and Blu-ray discs. This utility supports relatively long file names (127 characters for DVD), automatic parameter setting, image creation, project loading and saving, simple file management thanks to drag-and-drop option and many other functions. The program works with most recording devices.