I just don't know enough about computing and multimedia etc. to count myself qualified to comment on this following, but I'd be interested in reading the feedback from others who might have more experience and knowledge in this area.
A Cost Analysis of Windows Vista Content Protection
===================================================
Peter Gutmann, pgut001@cs.auckland.ac.nz
http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt Last updated 23 December 2006
SNIP
Disabling of Functionality
--------------------------
Vista's content protection mechanism only allows protected content to be sent
over interfaces that also have content-protection facilities built in.
Currently the most common high-end audio output interface is S/PDIF
(Sony/Philips Digital Interface Format). Most newer audio cards, for example,
feature TOSlink digital optical output for high-quality sound reproduction,
and even the latest crop of motherboards with integrated audio provide at
least coax (and often optical) digital output. Since S/PDIF doesn't provide
any content protection, Vista requires that it be disabled when playing
protected content. In other words if you've invested a pile of money into a
high-end audio setup fed from a digital output, you won't be able to use it
with protected content. Similarly, component (YPbPr) video will be disabled
by Vista's content protection, so the same applies to a high-end video setup
fed from component video.
Indirect Disabling of Functionality
-----------------------------------
As well as overt disabling of functionality, there's also covert disabling of
functionality. For example PC voice communications rely on automatic echo
cancellation (AEC) in order to work. AEC requires feeding back a sample of
the audio mix into the echo cancellation subsystem, but with Vista's content
protection this isn't permitted any more because this might allow access to
premium content. What is permitted is a highly-degraded form of feedback that
might possibly still sort-of be enough for some sort of minimal echo
cancellation purposes.
The requirement to disable audio and video output plays havoc with standard
system operations, because the security policy used is a so-called "system
high" policy: The overall sensitivity level is that of the most sensitive data
present in the system. So the instant any audio derived from premium content
appears on your system, signal degradation and disabling of outputs will
occur. What makes this particularly entertaining is the fact that the
downgrading/disabling is dynamic, so if the premium-content signal is
intermittent or varies (for example music that fades out), various outputs and
output quality will fade in and out, or turn on and off, in sync. Normally
this behaviour would be a trigger for reinstalling device drivers or even a
warranty return of the affected hardware, but in this case it's just a signal
that everything is functioning as intended.
Decreased Playback Quality
--------------------------
Alongside the all-or-nothing approach of disabling output, Vista requires that
any interface that provides high-quality output degrade the signal quality
that passes through it. This is done through a "constrictor" that downgrades
the signal to a much lower-quality one, then up-scales it again back to the
original spec, but with a significant loss in quality. So if you're using an
expensive new LCD display fed from a high-quality DVI signal on your video
card and there's protected content present, the picture you're going to see
will be, as the spec puts it, "slightly fuzzy", a bit like a 10-year-old CRT
monitor that you picked up for $2 at a yard sale. In fact the spec
specifically still allows for old VGA analog outputs, but even that's only
because disallowing them would upset too many existing owners of analog
monitors. In the future even analog VGA output will probably have to be
disabled. The only thing that seems to be explicitly allowed is the extremely
low-quality TV-out, provided that Macrovision is applied to it.
The same deliberate degrading of playback quality applies to audio, with the
audio being downgraded to sound (from the spec) "fuzzy with less detail".
Amusingly, the Vista content protection docs say that it'll be left to
graphics chip manufacturers to differentiate their product based on
(deliberately degraded) video quality. This seems a bit like breaking the
legs of Olympic athletes and then rating them based on how fast they can
hobble on crutches.
Full article posted at:
http://www.cs.auckland.ac.nz/~pgut001/pubs/vista_cost.txt