VOB can contain video, audio, subtitle and menu contents multiplexed together into a stream form. VOB is based on the MPEG program stream format, but with additional limitations and specifications in the private streams. The MPEG 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 program stream standard. While all VOB files are MPEG program streams, not all MPEG program streams comply with the definition for a VOB file.
On the DVD, all the content for one title set (VTS) is contiguous, but broken up into 1 GiB 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. Other DVD files include IFO and BUP files.