Logical format and UDF file system
All DVD formats – DVD-Video, DVD-Audio and Super Audio CD – are based on the DVD logical format. This is a key point differentiating DVD from the CD family, in which CD-ROM is a separate format from CD-Audio. Every DVD disc is a DVD-ROM disc and can be interpreted as a set of computer-readable files. The corollary of this is that every DVDplayer is, to at least some degree, a computing device capable of reading a file system and performing various actions in response to the data found in the files.
The file system used in DVD is Universal Disc Format (UDF). UDF was designed specifically for optical media and is an evolution of the ISO-9660 format that became a standard for CD-ROM applications after the initial years of confusion. UDF defines how the file system is implemented to facilitate use in an optical, replicated format, and to permit use with DOS, OS/2, Macintosh, Windows and UNIX operating systems.
As used in DVD, the UDF file system is constrained to a specific logical sector size (2048 bytes). DVD-Video imposes a number of additional constraints to facilitate the use of the file system in an inexpensive playback device, such as a set-top player. These constraints, contained in an appendix to the OSTA specification, are referred to as ‘micro-UDF’.
Like CD-ROM, DVD-ROM is a large information container that may be used to store a vast array of applications and files in a variety of formats, including text and word processing documents, database and spreadsheet files, multimedia presentations, digital audio, graphics and video, HTML pages, and browsers supporting Web connectivity. Thus, storing content for DVD-Video and DVD-Audio playback is only one aspect of DVD-ROM’s overall utility.
To ease implementation in inexpensive players, the DVD specifications include predefined directory locations on DVD-ROM discs for DVD-Video and DVD-Audio use. DVD-Video players look for all of their data in a ‘Video_TS’ directory, whilst DVD-Audio players can look in both Video_TS and ‘Audio_TS’ directories.
Material on a DVD that is stored outside of these directories is said to reside in the ‘DVD-Others zone’ of the disc, and is effectively invisible to a DVDVideo or DVD-Audio player. Such material is, however, completely accessible to a computer-hosted DVD-ROM drive. Because all DVD formats are based on DVD-ROM, DVD offers the ability to create hybrid discs that play back on inexpensive DVD-Video and DVD-Audio devices, whilst simultaneously delivering added-value material in computer-based settings.
Figure 3.1 An internal DVD-ROM drive installed in a computer.
DVD-ROM readers
All DVD-ROM readers (drives) will also read CD-ROM discs. To play a DVD-Video title in a DVD-ROM-equipped computer, the machine must not only include a DVD-ROM drive, but also have the ability to decode the audio and video formats mandated in the DVD-Video specification. At the time of this writing, virtually all personal computer manufacturers, including Apple, Compaq, Dell, Gateway, IBM, Hewlett-Packard, NEC, Sony, and Toshiba are offering DVD-Video capable models.
The complexity of DVD-Video’s video and audio formats means that decoding and output operations can place substantial demands on the computational resources of a computer. Initially most PC manufacturers elected to use hardware-based DVD decoding technology, but with today’s extremely fast CPUs (often optimized for multimedia), it is possible for DVD content to be processed in software alone, or using ‘hardware-assisted software’ decoding. Consumers upgrading existing PCs, however, are generally sold DVD-specific hardware decoding kits that are based on an add-in card.
Just as computer-hosted playback solutions became available for DVD-Video as that format took off, DVD-Audio solutions should begin to appear in 2001 as the new format is launched.
Web connectivity and eDVD™
As described in the previous section, the presence of zones on a DVD disc allows the design of hybrid titles, which give users with DVD-ROM drives access to additional content that is not in DVD-Video or DVD-Audio format. Among the most popular uses of hybrid titles is Web connectivity, where an application is included in the DVD-Others zone (a custom browser, for instance) that has the capability to dial up the publisher’s Web site. This allows a DVD publisher to link media content stored on a disc (motion video, audio, graphics) with additional dynamic content (updated information) delivered over the Web.
With a Web-connected DVD, the user essentially gets the best of both worlds: a rich multimedia environment (from the DVD) and up-to-the-minute information (from the Web). A DVD-Video concert title, for instance, might include a browser that, when launched in a DVD-ROM drive, automatically links the user to the concert artist’s section on a record label website. The section could include tour information, samples of songs from the artist’s recordings, and merchandise such as CDs, T-shirts and posters. The site might also include a chat area for the artist’s fans, a schedule of special Web-cast interviews with the artist, and preview tracks from upcoming releases.
While the user’s activities with a browser stored in the DVD-Others zone of a disc could be separate from actually watching content (a movie, for instance) stored in the DVD-Video zone, the benefit to the user may be enhanced by integrating the content from the two zones into a single experience. Sonic’s eDVD™, for example, allows DVD-Video to play back from a page in a Web browser, and lets the author of the DVD create links between the DVD-Video content and other elements of the page.
Figure 3.2 Using eDVD links, a window containing content from a DVD-Video title plays back from a Web page displayed in a browser.
Applications for eDVD exist in both entertainment and corporate/institutional markets for DVD. A historical drama, for instance, might include links to a Web site offering news accounts and interviews with those who participated in the actual events depicted in the movie, or to a commerce site with books on the same subject. A sales presentation with full-screen video and surround sound could play inside a Web browser from a page that also links to an online product information database and order-taking system, allowing a salesperson in the field instantly to place an order as they close a deal. Or a training program might integrate browser-based text and form-based (HTML) quizzes with rich audio-visual demonstrations.
By facilitating synergy between the media-rich environment of DVD and the flexible, up-to-the-minute interactivity of the Web, eDVD expands the interactive design possibilities of hybrid DVDs. The eDVD technology works directly with the operating-system-specific implementations that support DVD playback on computers. On the Microsoft Windows platform (Windows 98 and higher), eDVD acts via the DirectShow applications programing interface (API). On Mac OS computers, DVD-Video can be played from an eDVD Web page, but the video is displayed in the standard Apple DVD player, outside of the browser window.
DVD extensions: sDVD™, cDVD™, and hDVD™
The fact that all members of the DVD family are DVD-ROMs at heart is what allows the integration of content on a DVD-Video or DVD-Audio title with content on the Web, effectively extending the capabilities of DVDs used in a computer-hosted context. The flip side of this concept – using DVD to extend the capabilities of the Web – is the idea behind Streaming DVD (sDVD™).
With sDVD, the contents of a DVD-Video title are freed from the requirement of residing on a DVD disc. Instead, the source assets are data-reduced to bit rates tailored for streaming over networks. The sDVD streams retain the interactivity of the original DVD content, but are viewable over broadband Internet connections and intranets.
The data-reduction process is handled by authoring tools from Sonic Solutions. Once authored, sDVD content may be published on the Internet through an FTP upload to a standard web server, or streamed directly from the desktop using a Sonic utility called PersonalBroadcaster™. To read sDVD content, the computer uses a PC-based DVD player application.
While sDVD brings DVD-style presentations to networks, another DVD extension enables DVD-Video content to be played back on computers equipped with CD-ROM rather than DVD-ROM drives. Dubbed cDVD™, the technology uses CD-ROM discs – pre-recorded or CD-Rs – which are formatted as DVD-Video discs.
For programing that requires only the capacity of a CD-ROM (650 MB), cDVD will allow DVD-Video content to reach computer users who are not yet equipped with DVD-ROM drives. Since DVD-ROM drives also read CD-ROMs, the same discs are also playable on DVD-ROM equipped computers (although not in current set-top DVD-Video players). cDVD playback requires a software-only DVD player, which is automatically embedded in the DVD-Others zone of a cDVD by authoring tools from Sonic Solutions.
A third extension to DVD is hDVD™, which expands the video capabilities of DVD to include all formats supported by the ATSC DTV standard, not only Standard Definition (SD) but also High Definition (HD). Therefore, DVD may be used for computer-based delivery of video in formats such as 720p and 1080i (p: progressive video; i: interlaced video), with all the interactivity and functionality of a regular DVD-Video title. The amount of HD material that may be stored on an hDVD depends on the resolution of the video format used. hDVD authoring capabilities are available in authoring tools from Sonic Solutions, while hDVD-capable software DVD players handle the playback of hDVDs on computers.