There is a single file format specified for use with all the DVD Books A - D.This file system is the UDF/ISO-9660 Bridge format. UDF (Universal Disc Format) was designed specifically for optical media and has evolved from the ISO-9660 format. The benefit of this single file system is the ability for the DVD media to be compatible across set top players and personal computers with DVD ROM players.

The top level of organisation on a DVD disc is a volume. The volume contains a single DVD Video zone which contains all the data elements for the set-top video title, and a DVD others zone which can be used for non-DVD-video data elements such as desktop computer applications. It is important to note that currently set top players cannot accss the DVD Other zones as they only know how to access the DVD video zone. Computers can access the DVD Other zones and run applications that allow for a fuller interaction with the DVD Video zone.

DVD Volume structure

At the top of the structure is the DVD as a whole with its DVD other and video zone. Within the DVD video zone is the video manager, which is a master directory for the data elements, followed by 1 to 99 video title sets which inclue the video and audio elements. The video manager usually includes an introductory clip of video such as a logo, and a menu for navigation.

Video Title sets and Video Objects

Following the video manager are the video title sets. A DVD can contain multiple title sets. A Video Title Set (VTS) is made up of a VTS Menu, and one or more video titles. Titles in turn can be broken down into Parts of Titles (PTT). The data within the video title is made up of Video Object Sets (VOBS), which are made up of one or more Video Objects (VOB). A video object is made up of the video audio, navigation data and subpictures for a programme. It is the VOB which is the fundamental media file element of the DVD disc. The lowest branch of the DVD structure is the cell. Each VOB can be broken down into one or more cells. A cell may be as large as the entire movie or as small as an MPEG GOP (Group of Pictures).

For example a movie with 5 chapters would have one video manager, one title set, one title, one VOBS made up of one VOB and 10 cells. Multiple Title Sets and VOBS become apparent when interactive titles are created.

A DVD that included an interactive music video programme with ten artists, each with five videos, artist information. In this case the disc would have: on video manager, ten Video Title Sets, multiple Titles for each video. The reason for this division is that the DVD remote control has both Title and Menu buttons. The user can click on the Title button to return to the main DVD menu to select a title, or click on the Menu button to go to the menus for the particular title being viewed.

Kevin Round is a Director of Cofiant, a video editing and dvd authoring company based in the UK.