True to my word, I set out yesterday to test HD video decode acceleration on a Radeon HD 2900 XT using an HD DVD drive and a version of PowerDVD supplied by AMD for such purposes. To my surprise, CPU utilization during playback on our Core 2 Extreme X6800 test system ran between 40 and 50%, well above what one would expect from a solution with full HD video decode acceleration.
Naturally, I contacted AMD to inquire about the problem. I received a reply from AMD's David Baumann discussing the issue that ended with this revelation:
Be aware, though, that HD 2900 XT itself does not feature UVD, this is specific to 2600 and 2400, so the levels of CPU utilization you see should be somewhat similar to the previous generation.The UVD logic handles the CPU-intensive bitstream processing and entropy decode acceleration portions of the HD video playback pipeline. These are the most notable video decode acceleration capabilities that would separate the Radeon HD 2900 series from its direct competition, the GeForce 8800 series, if the HD 2900 XT actually had them. Turns out it does not. As the email states, the video playback capabilities of the Radeon HD 2900 XT are essentially similar to those of the previous-gen Radeon X1950.
So the essence of our correction is that the Radeon HD 2900 XT doesn't offer robust acceleration of HD video playback and will not likely reduce CPU utilization or power consumption substantially during high-definition video playback versus a GeForce 8800. We still intend to follow up with testing, but the lack of UVD logic on the GPU resets our expectations dramatically.
With that out of the way, I believe I ought to take a moment to explain how we came to believe the Radeon HD 2900 XT had full HD video playback acceleration, an impression formed by many layers of talk from AMD, starting with the Radeon HD name. Let me share a slide with you from a presentation titled "ATI Radeon HD 2000 Series and the Ultimate HD Experience," given by AMD's David Cummings, Director of Mobile GPU Marketing. The slide looks like so:
Now, look at any specs list for the Radeon HD 2900 XTsay, this one from AMD's website, and you will find listed among its specs "ATI Avivo™ HD Video and Display Platform" and a bullet point under that saying "HD decode acceleration for H.264/AVC, VC-1, DivX and MPEG-2 video formats." At the end of the day, one gets the impression that this GPU has Avivo HD, with all that entails.
Of course, AMD has left itself some wiggle room in its technical statements. The specs list above isn't technically untruejust imprecise. The dodge built into the Cummings presentation, with its talk of making HD video playback "accessible at all price points" seems to be that high-end CPUs can handle HD video playback without as much assistance from the GPU. But that's a paper thin excuse, in my view.
To make sure this wasn't simply a matter of me missing the boatit has been known to happen, and I've got a few gray hairs promising more of the same in the futureI checked with a couple of other journalists who attended a separate Radeon HD press event the week after the one I attended. Both Marco Chiappetta from HotHardware and Ryan Shrout of PC Perspective came away from their meetings with AMD convinced the Radeon HD 2900 XT had full HD playback acceleration via UVD logic, as well. I was not alone in gathering this impression from AMD. To their credit, some reviewers did sort through the fog and identify the Radeon HD 2900 XT's lack of UVD, but they were swimming against the tide of statements from AMD itself.
Nor could any of us have uncovered this fact prior to the publication of our reviews via testing, because AMD hasn't yet delivered a driver that includes the support for the Radeon HD's "full" multimedia capabilities. They initially targeted May 9 for that driver's release. AMD now says the driver is due next week.