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Wednesday, January 24, 2007
Microsoft clarifies Windows Vista Content Protection Measures


Following an interesting paper that raised questions about the content protection features in Windows Vista, Microsoft has clarified a number of points about the content protection measures present in the new operating system.

The paper was published by Peter Gutmann, a professor in the Department of Computer Science University of Auckland. Using logical arguments and simple language, Gutmann wrote down his thoughts about Vista's content protection schemes and came up with sharp conclusions that apparently did not leave Microsoft untouched.

As it is widely discussed, Windows Vista includes an extensive reworking of core OS elements in order to provide content protection for so-called "premium content", typically HD data from Blu-Ray and HD-DVD sources.

"Providing this protection incurs considerable costs in terms of system performance, system stability, technical support overhead, and hardware and software cost. These issues affect not only users of Vista but the entire PC industry, since the effects of the protection measures extend to cover all hardware and software that will ever come into contact with Vista, even if it's not used directly with Vista (for example hardware in a Macintosh computer or on a Linux server), " said Gutmann.

In a post on the Windows Vista Team blog, Microsoft has clarified a number of points about the content protection measures present in Windows Vista.

The post by Dave Marsh, Lead Program Manager for Video, provides some background to the issues surrounding content protection in Vista and also includes a very interesting FAQ. The FAQ provides answers to some questions that many people are asking about how Windows Vista will protect premium digital content and how this will affect users and programmers alike.

Here are some of the questions and answers.

Do these content protection requirements apply equally to the Consumer Electronics industry supplied player devices such as an HD-DVD or Blu-Ray player?

Generally the requirements are equivalent for all devices. For example, an HD-DVD or Blu-Ray disc always requires HDCP protection for DVI/HDMI outputs regardless of the type of device playing the disc. There are some cases, such as DVD-Video, where PCs have slightly different protection requirements than CE devices, but these differences are mainly historical and as dictated by the licenses associated with the systems providing access to the content (e.g., CSS for DVD).



This means that it's a level playing field and Vista isn't imposing any additional content protection burden on users. The same issues will be be possibly present on Windows and Mac and any consumer electronic devices.

When are Windows Vista's content protection features actually used?

Windows Vista's content protection mechanisms are only used when required by the policy associated with the content being played.

Microsoft claims here that it's not Windows that decides whether the content is protected or not, it's the publisher (Hollywood).

Will the playback quality be reduced on some video output types?

Image quality constraints are only active when required by the policy associated with the content being played, and then only apply to that specific content -- not to any other content on the user's desktop. As a practical matter, image constraint will typically result in content being played at no worse than standard definition television resolution. In the case of HD optical media formats such as HD-DVD and Blu-Ray, the constraint requirement is 520K pixels per frame (i.e., roughly 960x540), which is still higher than the native resolution of content distributed in the DVD-Video format. We feel that this is still yields a great user experience, even when using a high definition screen.

Microsoft admits that unless users have the appropriate hardware, the downgrade will take HD content down to about 960?540.

Do things such as HFS (Hardware Functionality Scan) affect the ability of the open-source community to write a driver?

No. HFS uses additional chip characteristics other than those needed to write a driver. HFS requirements should not prevent the disclosure of all the information needed to write drivers.

In order to prevent the creation of hardware emulators of protected output devices, Vista requires a Hardware Functionality Scan (HFS) that can be used to uniquely fingerprint a hardware device to ensure that it's genuine. In order to do this, the driver on the host PC performs an operation in the hardware (for example rendering 3D content in a graphics card) that produces a result that's unique to that device type. Obviously anyone who knows enough about the workings of a device to operate it and to write a third-party driver for it (for example one for an open-source OS, or in general just any non-Windows OS) will also know enough to fake the HFS process. The only way to protect the HFS process therefore is to not release any technical details on the device. But Microsoft claims here that HFS requirements should not prevent the disclosure of all the information needed to write drivers.

Will Windows Vista content protection features increase CPU resource consumption?

Yes. However, the use of additional CPU cycles is inevitable, as the PC provides consumers with additional functionality. Windows Vista's content protection features were developed to carefully balance the need to provide robust protection from commercial content while still enabling great new experiences such as HD-DVD or Blu-Ray playback.

Aren't there already output content protection features in Windows XP?

Yes. Output content protections are not new requirements for commercial content. The CSS content protection system for DVD-video discs requires output protections such as Macrovision ACP and limiting the resolution on component video outputs to standard definition. Windows XP has supported these requirements for some time.

Is content protection something that is tied to High Definition video?

While HD content has some unique content protection requirements, many of the requirements apply to commercial content generally, independent of resolution.

What about S/PDIF audio connections?

Windows Vista does not require S/PDIF to be turned off, but Windows Vista continues to support the ability to turn it off for certain content -- a capability that has been present on the Windows platform for many years. Additionally, in order to support the requirements of some types of content, Windows Vista supports the ability to constrain the quality of the audio component of that content. Similar to image constraint for video, this quality constraint only applies to the audio from content whose policy requires the constraint, not to any other audio being played concurrently on the system. As a practical matter, these audio restrictions are not widely used today.

Will Component (YPbPr) video outputs be disabled by Windows Vista's content protection?

Similar to S/PDIF, Windows Vista does not require component video outputs to be disabled, but rather enables the enforcement of the usage policy set by content owners or service providers, including with respect to output restrictions and image constraint.

Will echo cancellation work less well for premium content?

We believe that Windows Vista provides applications with access to sufficient information to successfully build high quality echo cancellation functionality.

Will it mean that there will no longer be unified graphics drivers?

The Windows Vista content protection requirements for graphics drivers will not lead to movement away from unified drivers. In fact, all graphics drivers shipped with Windows Vista are unified drivers.

Will Windows Vista audio content protection mean that HDMI outputs can't be shown as S/PDIF outputs?

It is better if they show as different codec types, as it allows the difference to be reflected in the UI, thus providing the user help with their configuration and creating a better user experience. The user wants to know the difference between HDMI and S/PDIF, as they are different physical connectors.

What is revocation and where is it used?

Renewal and revocation mechanisms are an important part of providing robust protection for commercial audiovisual content. In the rare event that a revocation is required, Microsoft will work with the affected IHV to ensure that a new driver is made available, ideally in advance of the actual revocation. Revocation only impacts a graphics driver's ability to receive certain commercial audiovisual content; otherwise, the revoked driver will continue to function normally.

Does Windows Vista's use of OMAC-authenticated communication impact graphics driver performance?

The authenticated communication mechanisms used for Protected Video Path in Windows Vista are only actively used while commercial content is playing. This means that while there is a performance impact, it is limited to the scenarios where it is required to provide robust protection for commercial content.

Probably the most important issue here is that all these will affect not only users of Vista but the entire PC industry, since the effects of the protection measures extend to cover all hardware and software that will ever come into contact with Vista, even if it's not used directly with Vista (for example hardware in a Macintosh computer or on a Linux server). It seeems that it's a first class opportunity to "enforce" Windows as the sole solution for tasks related to computing.


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