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DVD Control Data Structure

This topic applies to Windows Media Player version 6.4 only.

DVD-Video content is organized in large chunks, called titles. A title can be further subdivided with predefined access points, called chapters (the technical term is Part_of_Title, or PTT). Each DVD-Video volume can contain up to 99 titles. Each title can have up to 99 or 999 chapters, depending on how the disc is authored. The Windows Media Player control provides seeking capabilities for DVD at three distinct levels, as outlined in Seeking in DVD.

DVD-Video Volume Structure

Control data Description
Video Title Set (VTS) Collection of movies. A single volume can contain from 1 to 99 video title sets.
Title Individual movie. This might be a simple, linear movie, consisting of one program chain, or it might consist of several program chains.
Program Chain (PGC) Collection of programs (often chapters in a movie). Possible options include different ratings, camera angles, or a different storyline.
Chapter/Part of Title (PTT) Access point at a cell boundary in a video stream used to create chapter access points. Can delimit scenes or provide optional scenes from which to choose.
Program (PG) Collection of cells, which typically make up a scene.
Cell Collection of Video Object Units (VOBUs) The minimum unit of access for branching navigation.
Interleave Unit (ILVU) Block of one or more VOBUs in a multiangle stream of video that contains video of only one angle.
Video Object Unit (VOBU) Group of pictures (GOP). Usually half a second of video.
Pack 2 KB of data, corresponding to a logical sector of the disc, consisting of only one media type (such as video or audio).

The DVD file system is different from a format like CD-ROM, which contains a linear series of tracks not easily customizable by the author. The author of DVD-formatted media files can control track layout and navigation much more precisely. Authors gain this control because the media file itself has many parts and control mechanisms that enable the author to arrange and rearrange the playback order as needed. You can locate a specific portion of a file by time (in hours, minutes, seconds, and frames) or by chapter value.

A media file is made up of a list of program chains (PGCs), each of which is made up of a list of programs, each of which is made up of a list of cells, each of which is made up of a list of video object units (VOBUs), each of which is made up of a list of packs, and each of which is made up of actual MPEG (Moving Picture Experts Group) data. The following graphic illustrates the DVD file system structure.

DVD file system structure

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