Video Decode Performance - Introduction

PureVideo HD decode on G84 is currently only usable under Vista x86. The implementation in the Vista x64 driver is problematic to say the least, and it's simply not available for XP yet, and won't be until June. So if you're looking for your HD video decode fix with this GPU, your current platform at the time of writing is clear. NVIDIA's PVHD technology isn't implemented under non-Microsoft OSes at this stage, either.

The test setup comprised a fresh installation of Vista Business x86 with all available Windows Update patches and fixes applied. We recorded processor utilisation (as a whole, for both user- and kernel-mode code) using a simple tool during playback of a scene in chapter 15 of Harry Potter and the Goblet of Fire on HD-DVD. HP:GOF is a VC-1 title, AACS protected and native 1080p, and the scene we measure has an average bitrate of nearly 20Mib/sec over three minutes.

WinDVD 8.0 (8.221 Beta, provided by NVIDIA) was the playback software. It's the only software able to hook into the DXVA path for making use of the PureVideo HD technologies in G84 at the current time, PowerDVD 7.2 showing scaling and deinterlacing artifacts and poorer performance, indicating it uses the 'common' DXVA path at the current time.

Remember that the base clock (and thus the clock for the PVHD blocks) was 730MHz on the test 8600 GTS used, since that'll have some effect on video performance. Unfortunately there's no readily available tool that adjusts G84 base clock frequency so we could measure the effect of the 730MHz clock versus the stock 675MHz.

Performance was measured while the HD-DVD was being played back was being run full-screen on a Dell 3007 display (30", supports HDCP, 2560x1600), which isn't possible with any other consumer graphics hardware at the time of writing. Hardware like GeForce 8800 GTX or ATI Radeon X1950 XTX, despite being more powerful in terms of general performance, only supports HDCP on one of its dual DVI links, per DVI port. The Dell 3007's HDCP support with one link is limited to running the display at 1280x800 (one quarter the native resolution) with simple pixel scaling. Image quality under those conditions is unacceptable for that panel, since it has no video scaler.

While the number of people looking to use the Dell 3007 and similar displays as a HDTV (even part of the time) is minimal, it's a niche market that GeForce 8600 GTS addresses, and addresses alone at the time of writing. Let's see how the hardware does decoding our test AACS-encrypted VC-1 HD-DVD.

The following images from Cyberlink's HD readiness tester highlights what happens. Firstly, 8600 GTS running the panel at 2560x1600.

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The tester isn't sure about the 8600 GTS as a product it knows about, but HDCP is shown as active. GeForce 8800 GTX at 2560x1600 is next.

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The 8800 GTX can't protect both DVI links here and HDCP is therefore shown as inactive. That's the case for everything other than 8600 GTS, and with WinDVD, playback fails with a handy Stop message. Drop down to 1280x800 however, and HDCP is active on the single link.

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We test 8600 GTS running the HD-DVD full-screen on the big Dell.