A
conversation has cropped up since the recent publication of a paper
scrutinizing how Windows handles digital rights management, especially
for HD video. I've since looped back with Dave Marsh, a Lead
Program Manager responsible for Windows' handling of video, to learn
from him the implications involved and to learn to what extent the
paper's assertions are accurate. The following is an article Dave
has put together to address the misconceptions
in the paper, followed by answers to what we expect will be the most
frequent questions in the minds of our customers. Leave us a
comment to let us know what you think. -- Nick
Over the holidays, a paper was
distributed that raised questions about the content protection features
in Windows Vista. The paper draws sharp conclusions about the
implications of those features for our customers. As one of the
Lead Program Managers for the technologies in question, I would like to
share our views on these questions.
Windows Vista includes content
protection infrastructure specifically designed to help ensure that
protected commercial audiovisual content, such as newly released HD-DVD
or Blu-Ray discs, can be enjoyed on Windows Vista PCs. In many
cases this content has policies associated with its use that must be
enforced by playback devices. The policies associated with such
content are applicable to all types of devices including Windows Vista
PCs, computers running non-Windows operating systems, and standalone
consumer electronics devices such as DVD players. If the policies
required protections that Windows Vista couldn't support, then the
content would not be able to play at all on Windows Vista PCs.
Clearly that isn't a good scenario for consumers who are looking to
enjoy great next generation content experiences on their PCs.
Associating usage policies with
commercial content is not new to Windows Vista, or to the
industry. In fact, much of the functionality discussed in the
paper has been part of previous versions of Windows, and hasn’t
resulted in significant consumer problems – as evidenced by the
widespread consumer use of digital media in Windows XP. For
example:
- Standard definition DVD playback has
required selective use of Macrovision ACP on analog television outputs
since it was introduced in the 1990s. DVD playback on and in
Windows has always supported this.
- The ability to restrict audio outputs
(e.g., S/PDIF) for certain types of content has been available since
Windows Millennium Edition (ME) and has been available in all
subsequent versions of Windows.
- The Certified Output Protection
Protocol (COPP) was released over 2 years ago for Windows XP, and
provides applications with the ability to detect output types and
enable certain protections on video outputs such as HDCP, CGMS-A, and
Macrovision ACP.
It's important to emphasize that while
Windows Vista has the necessary infrastructure to support commercial
content scenarios, this infrastructure is designed to minimize impact
on other types of content and other activities on the same PC.
For example, if a user were viewing medical imagery concurrently with
playback of video which required image constraint, only the commercial
video would be constrained -- not the medical image or other things on
the user's desktop. Similarly, if someone was listening to
commercial audio content while viewing medical imagery, none of the
video protection mechanisms would be activated and the displayed images
would again be unaffected.
Contrary to claims made in the paper,
the content protection mechanisms do not make Windows Vista PCs less
reliable than they would be otherwise -- if anything they will have the
opposite effect, for example because they will lead to better driver
quality control.
The paper implies that Microsoft decides
which protections should be active at any given time. This is not
the case. The content protection infrastructure in Windows Vista
provides a range of à la carte options that allows applications
playing back protected content to properly enable the protections
required by the policies established for such content by the content
owner or service provider. In this way, the PC functions the same
as any other consumer electronics device.
With that introduction, here are the top
twenty questions, and answers, that aim to address some of the other
points raised in the paper.
Dave Marsh - Lead Program Manager for Video
Twenty 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).
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. For Windows Vista experiences, if the
content does not require a particular protection, then that protection
mechanism is not used.
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.
Will this affect things like medical imagery applications?
Image constraints only apply to
protected content being played and not to the desktop as a whole;
therefore, the resolution of other non-protected media, such as medical
images, is not affected.
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.
Will the Windows Vista content
protection board robustness recommendations increase the cost of
graphics cards and reduce the number of build options?
Everything was moving to be integrated
on the one chip anyway and this is independent of content protection
recommendations. Given that cost (particularly chip cost) is most
heavily influenced by volume, it is actually better to avoid making
things optional through the use of external chips. It is a happy
side effect that this technology trend also reduces the number of
vulnerable tracks on the board.
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 this complicate the process of writing graphics drivers?
Adding new functionality usually
introduces new complexity. In this case, additional complexity is
added to the graphics driver, but that complexity comes with the direct
consumer benefit of new scenarios such as HD-DVD or Blu-Ray playback.
Will the 'tilt bit' mechanism cause
problems even when the driver is not under attack from a hacker, e.g.,
when there are voltage spikes?
It is pure speculation to say that
things like voltage fluctuations might cause a driver to think it is
under attack from a hacker. It is up to a graphics IHV to
determine what they regard as an attack. Even if such an event
did cause playback to stop, the user could just press 'play' again and
carry on watching the movie (after the driver has re-initialized, which
takes about a second). Again, it is important to note that this
could only occur in the case of watching the highest-grade premium
content, such as HD-DVD or Blu-Ray. In practice I doubt it would
ever actually happen.
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.
Do content protection requirements mean that graphics chips have to provide hardware acceleration for video decode?
No. The Windows Vista content
protection requirements do not require that graphics hardware include
hardware acceleration for decode for many years, but such support is
highly recommended to improve the user experience for HD content.
Will the video and audio content protection mechanisms affect gaming on the PC?
The Windows Vista content protection
features were design for commercial audiovisual content and are
typically not used in game applications. A game author would have
to specifically request these features for them to impact game
performance.