AnandTech takes a look at the hardware H.264 acceleration of the GeForce 8600. Nvidia – which normally always lags behind with these kinds of features – is ATi too fast in this case, but how well does it work?
H.264 is the heaviest of the three codecs supported by Blu-ray and HD DVD. It delivers good quality, but also demands a lot from the processor. Even a relatively fast dual-core can still have a lot of work to do when processing an HD stream. Older video chips can help with this a bit, but still leave the heavy lifting to the CPU. The recently released GeForce 8500/8600 cards are the first to feature full hardware H.264 decoding, including decrypting aacs security. Oddly enough, the more expensive GeForce 8800 doesn’t have this feature, nor is it clear if it will ever get it again.
To start with the test, AnandTech is struggling with software issues. PowerDVD and WinDVD do offer support for Blu-ray and HD DVD, but they still (regularly) suffer from crashes. All the way under the 64-bit version of Vista and in combination with the acceleration of ATi, the problems are very present. With a little perseverance they eventually manage to collect benchmarks for three HD films: Yozakura, The Interpreter and Serenity.
While displaying the first 105 seconds of the first movie without GPU acceleration, PowerDVD uses an average of 88% of the processing power of a Core 2 Duo E6320. With hardware decoding, consumption drops to around 21%. The much more expensive 8800 GTX leaves the processor under 65.4% load, because it has fewer features in this area than its little brothers. ATi’s current top card comes in at 75.2%. Overall, WinDVD is slightly more efficient than PowerDVD, but lacks support for ATi’s features and is therefore less interesting to compare. The second film shows about the same picture as the first. For the third film, the feature has less effect, because it was made with a different codec (VC-1). This codec is in any case less heavy than H.264 (purely software only requires 35.9% to be tapped) and the GPU can shave another ten percent off.
In addition to performance, power consumption is also discussed. On average, the system consumes 135.1 watts during decoding with the CPU and 124.8 watts with the GPU. A marginal difference, but in any case it is not the case that the savings made by the processor are negated by the video card. The bottom line is that there are no downsides to using hardware decoding, other than the still flimsy Blu-ray/HD DVD support in PC software. Especially the cheap GeForce 8500 is a very interesting option for builders of htpc systems. Although ATi is expected to release its own solution in this category very soon, it is positive for nVidia that they are not lagging behind this time.