Hardware Support

Digital Versatile Disk (DVD) provides digital data storage that encompasses audio, video, and computer data, and therefore has the potential for replacing current technologies for business data storage, laser disc, audio CD, CD-ROM, VHS videotape, and dedicated game technologies. DVD was designed for multimedia applications, with the goal of storing full-length feature movies.

The DVD Consortium has defined two major compression technologies, MPEG-2 and AC-3 (also called Dolby Digital), which you can use to store over two hours of video and audio on a single DVD disk. The quality of the stored video and audio is higher than that found on laser disks and CDs.

DVD Support

Windows 2000 Professional supports DVD as follows:

DVD Movie Playback    If the proper decoding hardware or software is present, Windows 2000 Professional supports playback of DVD video. This support is especially important for entertainment computers, but it is also important for any multimedia platform meant to provide good quality support for the playback of movies. This support includes the full range of interactivity and high-quality playback found on a standard DVD Video player. Because computers are capable of better image quality than television, playing DVD on a computer running Windows 2000 Professional can produce an image of better quality than standard DVD video player devices connected to a television set.

DVD as a Storage Device    You can use DVD as a storage device on most computers that support DVD. While most first-generation DVD-ROM drives do not read CD-Recordable (CD-R) disks, all second-generation drives do. DVD-ROM discs and devices provide cost-effective storage for large data files. There are a number of competing formats for rewritable DVD, such as DVD-RAM, DVD-RW, and DVD+RW. However, there is no single drive that is capable of reading all of these different types of media.

Figure C.2 shows the support architecture for existing DVD technologies that use Windows 2000 Professional.

Figure C.2 Implementation of the DVD support architecture

DVD Movie Playback Components

The following components comprise support for DVD movie playback under Windows 2000 Professional:

DVD-ROM Class Driver    DVD-ROM has its own industry-defined command set, supported through an updated CD-ROM class driver. This driver provides the ability to read data sectors from a DVD-ROM drive.

UDF File System    Support for Universal Disk Format (UDF) ensures support for UDF-formatted DVD discs. UDF takes advantage of packet writing and is the industry standard for compact disc storage. As with File Allocation Table (FAT) and FAT32 file systems, Windows 2000 Professional provides installable file systems for UDF.

WDM Stream Class Driver    The WDM Stream class driver supports streaming data types, and MPEG-2 and AC-3 (Dolby Digital) hardware decoders. Hardware vendors must write only a small amount of interface code in a minidriver to ensure that the specific features in their hardware are supported. This allows most DVD decoders to work without user intervention.

DirectShow    Microsoft DirectShow (formerly ActiveMovie) proxy filters and related support include a DVD Navigator/Splitter, proxy filters for video streams, a video mixer, and a video renderer. The proxy filters allow programs written to the DirectShow API to control kernel mode filters.

DirectDraw Hardware Abstraction Layer (HAL) with Video Port Extensions (VPE)    Decoded video streams are huge — possibly too large even for the PCI bus on a computer. Manufacturers have solved this problem by creating dedicated buses to transfer decoded video streams from an MPEG-2 decoder to the display card. Microsoft provides software support for these interfaces using the DirectDraw HAL with VPE.

Copyright Protection    Copyright protection for DVD is established when key sectors on a disk are encrypted , then decrypted before the sectors are decoded. The encryption scheme used is called the Content-Scrambling System (CSS). Microsoft provides support for both software and hardware decrypters using a software module that enables authentication between the decoders and the DVD-ROM drives in a computer.

Regionalization    As part of the copyright protection scheme used for DVD, the DVD Consortium has defined six worldwide regions. Disks are playable on DVD devices in some or all of the regions according to regional codes set by the content creators. Microsoft provides software that responds to the regionalization codes as required by the DVD Consortium and as part of the decryption licenses.

DVDPlay    Microsoft provides a DVD movie playback application, which you can replace with another DVD playback application written to DirectShow2.

DVD-ROM Storage Device

Under Windows 2000 Professional, DVD-ROM is simply a large storage medium, much like CD-ROM. To enable DVD-ROM as a read-only device, Microsoft provides support for DVD-ROM devices in Windows 2000 Professional and support for UDF as an installable file system. Using DVD-ROM device drivers, a DVD-ROM drive is treated as another peripheral, using industry-defined methods to access DVD disks and handle encrypted content.

DVD and Streaming Data

A program produces streaming data when it delivers large amount of data in a constant load, or stream, over time. The program never loads the data completely into memory; the data file might be too large, and the operations on the data file are typically sequential. The best example of this for DVD is an MPEG-2 video stream. When a computer plays an MPEG-2 file, a program loads and streams the MPEG-2 data through the computer for decoding and displaying. The data might enter and exit the host processor and bus of the computer several times during this process. In addition, an MPEG-2 stream starts out at approximately 5 to 10 Mbps. After the stream is decoded, the data transfer rate can easily exceed 100 Mbps. A single data stream this large can saturate and overwhelm a computers PCI bus, so an alternate path might be required for the raw, decoded video data.

A single stream demands a potentially large and constant load on a computer, over what can be considered a long time in computer terms. DVD is even more demanding because the system must be able to independently manage and decode at least four separate streams:

• MPEG-2 video

• AC-3 or MPEG-2 audio

• Subpicture

• Navigation

This independent processing of streams is necessary to ensure that the streams are totally synchronized when they reach their final destinations, with no dropped frames or degraded video. This requires precision in load balancing, synchronization, and processing.

The WDM Stream class driver can deal with these problems because it is optimized to work with any devices that use streamed data. This includes devices that encode data (for example, video capture devices), and those that decode data (for example, DVD hardware decoders that decode MPEG-2 streams for playing DVD movies). This class driver uses the WDM layered architecture for interconnecting device drivers to optimize data flow within the Windows 2000 Professional kernels.

For more information about DVD, see Multimedia in this book.