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DVD Overview

Digital video disc (DVD) represents the next generation in optical disc storage technology for video and audio computer data. Essentially, a DVD is a compact disc (CD) that provides increased storage capacity, faster data access, and superior playback quality. A DVD holds 4.38 gigabytes (4.7 billion bytes) of data on each side — enough for a movie more than two hours long. Each side can hold two layers of information, allowing a single DVD to hold up to 15.9 gigabytes (17 billion bytes) of audio, video, and other types of data. A CD-ROM of the same physical size holds 650 megabytes (682 million bytes) of data.

DVD aims to provide a unified solution for home entertainment, business, computer storage, and computer multimedia with a single digital format. Eventually, DVD aims to replace audio CD, videotape, laser disc, and CD-ROM technologies. Currently, DVD has widespread support from all major electronic companies, all major computer hardware companies, all major movie studios, and many major music studios. Thus, DVD technology has an excellent opportunity to revolutionize the distribution of media.

A DVD title can offer simultaneous multilingual support, parental control mechanisms, menu options, chapter searching, and varied viewing through multiple camera angles.

Note To use DVD playback with the Microsoft® Windows Media™ Player control, you need to have Microsoft® Internet Explorer 5, the Microsoft® Windows® 98 OEM Service Release (OSR), or Microsoft® Windows® 2000 installed.

This article contains the following sections.

DVD Interfaces

The Microsoft Windows Media Player control exposes the IMediaPlayerDvd interface through the DVD property. This interface enables the Windows Media Player control to access the Microsoft® DirectShow® DVD-specific properties, methods, and events.

DirectShow provides the following DVD-related interfaces.

InterfacePurpose
IDvdGraphBuilder Enables the DVD application writer to easily build a filter graph for DVD-Video playback.
IDvdControl Controls the playback and search mechanisms of a DVD-Video disc that contains one or more video movies.
IDvdInfo Enables an application to query for attributes of available DVD-Video titles and the DVD player status.

For more information on the DirectShow DVD-related interfaces, see Overview of DVD Interfaces and Data Types in the DirectShow Software Development Kit.

Later sections of this article group properties, methods, and events from the IMediaPlayerDvd interface into functional categories. For more information about DVD properties, see Using DVD Properties. For more information about DVD methods, see Using DVD Methods.

The Windows Media Player control also provides a number of event and error codes. For more information about event codes, see Using DVD Event Codes. For more information about error codes, see DVD Error Codes.

DVD Control Data Structure

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 Control Data Structure Diagram

DVD Features

This section outlines features specific to DVD-Video and lists the Windows Media Player control methods that provide these features. These features include the following:

Seeking in DVD

The Windows Media Player control enables you to seek at several different levels within DVD content. The DVD-Video disc format includes special data for seeking and navigation.

DVD-Video streams consist of .vob files and associated .ifo files that contain information for navigation and data searching, including random access, fast-forward and fast-backward play, angle switching, and seamless branching. In the case of One_Sequential_PGC_Titles, a time map table enables time-based seeking. For titles not authored in One_Sequential_PGC format, such as those with branching or multiple ratings, time-based seeking is not supported.

In contrast, MPEG-2 files play from the beginning or require access points to be specified as byte offsets into the file to Group of Pictures (GOP) headers. You can access any GOP without prior authoring of entry points, as is required in the case of DVD-Video chapters.

The following table shows the Windows Media Player control DVD-Video methods exposed for seeking at various levels.

Seeking level Control data IMediaPlayerDvd methods
Title Seeks Video Title Set (VTS), Title, Program Chain (PGC) TitlePlay
Chapter Seeks Chapter/Part of Title (PTT), Program (PG) ChapterPlay (specifying title and chapter number), ChapterSearch (search for a chapter within the same title), PrevPGSearch, TopPGSearch, NextPGSearch
Time Seeks Interleave Unit (ILVU), Video Object Unit (VOBU) TimePlay (start playing specified title from specified time), TimeSearch (start playing from specified time within the same title)

Subpicture

Subpictures are encoded graphics that can be displayed over the top of the video. The subpicture feature is decoded and alpha blended. The data on the alpha channel could be text for closed captioning, buttons to provide a user interface, menus, subtitles, credits, and so on. Each pixel in a subpicture graphic is encoded with 2 bits, allowing only four colors and four levels of transparency per pixel, chosen from palettes of colors and contrast levels.

Properties relating to the subpicture feature include the following:

The method relating to subpictures is GetSubpictureLanguage.

The event relating to subpictures is EC_DVD_SUBPICTURE_STREAM_CHANGE.

Multiple Language Support

DVD-Video provides support for up to eight audio tracks to accommodate various languages. DVD-Video also supports text in different languages for statistics related to the DVD title, such as cast, crew, and title. On-screen menus can be displayed in various languages.

Methods relating to language support include the following:

Variable Speed Play

The Windows Media Player control provides variable speed play, at both faster and slower speeds than normal, through the ForwardScan and BackwardScan methods.

Consumer DVD Interactivity

Consumers can interact with DVD titles by selecting and activating buttons and displaying menus. Buttons can be selected by clicking directly on the video window.

Methods relating to consumer interactivity include the following:

A mouse rollover causes a select, but is prevented from performing a select and activate action. A mouse click is required to activate the button because mouse movement on a PC differs from remote control tabbing on a consumer player.

Seamless Video Angle Change

DVD-Video supports up to nine camera angles. These angles can be completely independent video streams or different camera angles of the same scene. The fast seeking of the DVD disc enables you to switch angles seamlessly.

Properties relating to video angles include the following:

Events relating to video angles include the following:

Additional DVD Resources on the Web

The following list contains links to a few of the Web sites that provide DVD information. Search the Web for other DVD resources. Note that most of these external links point to servers that are not under Microsoft control. Please read Microsoft's official statement regarding other servers.

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