Vista users will need third-party software to play prerecorded HD DVD discs—the built-in Windows Media Player 11 and Media Center interfaces will not play them unless extra software is installed. Although this seems to counter Microsoft's pledge to support HD DVD in Vista, this is similar to how Windows XP works with regular DVDs. Microsoft quietly revealed the details about Vista's lack of HD DVD playback software in early 2006, but the story was not widely publicized until August and was clouded by an erroneous report of differences between 32-bit and 64-bit support.

Vista Support Similar to Windows XP

HD DVD is one of two competing and incompatible formats for high-definition video discs, along with Sony's Blu-ray. In Sept. 2005, Microsoft said that Windows Vista would have native support for HD DVD and not Blu-ray. The company subsequently announced partner support for HD DVD on Vista during its May 2006 Windows Hardware Engineering Conference (WinHEC), saying "Windows Vista will be shipped with the drivers, file system and other components necessary to support HD DVD playback."

However, in blog postings and interviews before WinHEC, as well as in a WinHEC breakout session, Microsoft explained that Vista itself will not include the HD DVD decoder software required to play HD DVDs. Instead, customers will have to get additional software from third parties such as Cyberlink, InterVideo (which is being acquired by Corel), Roxio, and Sonic Solutions. Some of these third-party products will integrate with Vista's Media Center interface, making it possible to play HD DVDs from Media Center after the third-party software is installed.

Microsoft did not explain why it is not including HD DVD playback in Vista. However, if somebody had used playback software in Vista to crack the copy-protection on HD DVDs, Microsoft might have been exposed to lawsuits. Another possibility is that Microsoft doesn't want to pay royalties to ship HD DVD decoding software with every copy of Vista, although Microsoft owns some patents related to HD DVD and would have received a cut of these royalties.

Vista's lack of HD DVD playback software is similar to the situation with regular DVDs: customers must rely on third-party Windows Media Player plug-ins or stand-alone players to play DVDs on Windows XP PCs.

In practice, few consumers have been affected by the lack of DVD playback software in Windows XP because DVD drive manufacturers bundle the necessary software or OEMs add the software when they include a DVD drive. A similar outcome is likely with HD DVD. For that matter, although Microsoft currently has no plans to support Blu-ray, any OEM that ships a PC with a Blu-ray drive will almost certainly ship all the software necessary to play Blu-ray discs.

No Difference on 64-Bit

Contrary to an Aug. 2006 report, it seems unlikely that there will be any difference in how 32-bit and 64-bit Windows Vista systems treat HD DVDs or Blu-ray discs.

Vista will expose a list of any unsigned drivers on the system. This list of unsigned drivers can be used by third-party software—including third-party HD DVD and Blu-ray plug-ins and players—to determine whether playback of high-definition video content will be enabled or not. For example, a movie studio could dictate that none of its high-definition discs should play on any Vista PC with an unsigned video card driver, and an ISV could create a software application that honors this restriction.

64-bit drivers, which are typically newer due to the recent availability of 64-bit processors and 64-bit Windows clients, must be signed for Vista to load and use them, while older 32-bit drivers are typically unsigned. Because of this discrepancy, it's possible that ISVs, on the behalf of content owners, will prevent high-definition discs from playing on 32-bit Vista systems. However, no such plans have been announced, and such a move would limit the audience for high-definition discs—a risky move when trying to establish a new format.

Microsoft's announcement of support for HD DVD is covered in "HD DVD Gets Microsoft Backing" on page 29 of the Nov. 2005 Update.

Microsoft's home page for Windows Media Player 11 is www.microsoft.com/windows/windowsmedia/player/11/using.mspx.

The May 2006 WinHEC press release about HD DVD is at www.microsoft.com/presspass/press/2006/may06/05-24WinHECHDDVDPR.mspx.

The Windows Vista team's blog discusses the issue of high-definition video playback at blogs.technet.com/windowsvista/archive/2006/08/24/450081.aspx.