VOB

A VOB file (Video Object) is a container format in DVD-Video media. VOB can contain video, audio, subtitle and menu contents multiplexed together into a stream form. VOB is based on MPEG-2 Program stream format, but with additional limitations and specifications in the private streams. The MPEG-2 Program stream has provisions for non-standard data (as used in VOB files) in the form of so-called private streams. VOB files are a very strict subset of the MPEG-2 Program stream standard. While all are MPEG-2 Program streams, not all MPEG-2 Program streams comply with the definition for a VOB file.

Analogous to MPEG-2 Program stream, VOB file can contain MPEG-2 Part 2 or MPEG-1 Part 2 video, MPEG-1 Audio Layer II or MPEG-2 Audio Layer II audio, but usage of these compression formats in VOB file has some restrictions in comparison to MPEG-2 Program stream. In addition, VOB can contain Linear PCM, AC-3 or DTS audio and subpictures (subtitles). VOB file cannot contain AAC audio (MPEG-2 Part 7), MPEG-4 compression formats and others, which are allowed in MPEG-2 Program stream standard.

On the DVD, all the content for one title set (VTS) is contiguous, but broken up into 1 GB VOB files in the computer compatible file systems for the convenience of the various operating systems. Each VOB file must be less than or equal to one GB (1024x1024x1024 Bytes = 1,073,741,824 Bytes).

Other DVD files include IFO and BUP files. IFO (Info) files contain all the information a DVD player needs to know about a DVD so that the user can navigate and play all DVD content properly (e.g., where a chapter starts, where a certain audio or subtitle stream is located, information about menu functions and navigation, etc.). BUP (Backup) files are an exact copy and backup of IFO files in case of corruption. VOB files without IFO or BUP files do not allow DVD menu navigation. Images, video and audio used in DVD menus are stored in VOB files.

The article is based on materials from matroska.org, wikipedia.org.