X-bit labs

Ready to HD: Performance of Contemporary Graphics Accelerators during Video Playback (page 6)

Category: Video

by Alexey Stepin , Yaroslav Lyssenko, Anton Shilov

[ 02/26/2007 | 05:24 PM ]

Test Results

Premium Graphics Cards

Playing DVDs is long not a problem for modern, and even some not-very-modern, graphics cards. Every graphics solution can decode this format at a CPU load of less than 5.5%.

MPEG-2 being a rather simple format, the decoding of a 20Mbps video stream with a frame resolution of 1920x1080 pixels is not a problem for today’s CPUs and graphics subsystems. In the worst case the CPU is loaded by only 16%, most of its resources being left free for other tasks. The GeForce 8800 series copes with this task better than its opponents, obviously due to the extremely high frequency of the pixel processors, over 1GHz. Note also how low the 8800 series cards keep the average CPU load.

The DivX format demands more computing power even when the frame resolution is as low as 640x480. Here, Avivo technology represented by the Radeon X1950 XTX proves to be superior. Strangely enough, the new generation of GeForce cards is the slowest of all at decoding this video content. Perhaps this is due to some flaws in their drivers.

When processing a clip in a HD resolution and encoded with XviD, the Radeon X1950 XTX cannot keep the CPU load as low as at 640x480 resolution.

The flagship products from AMD and Nvidia take up about the same amount of work when DivX HD content is being decoded. A load of 40% is not low for a rather advanced dual-core CPU, but the playback conditions are comfortable anyway. At least there is no jerkiness or lost frames. The GeForce 7950 GX2 is somewhat worse than the other premium-class solutions because SLI technology doesn’t provide any advantages for decoding video whereas the frequency of this graphics card’s cores is 500MHz which is far lower than that of the Radeon X1950 XTX and GeForce 8800.

H.264 is a complex format, but the hardware support for its decoding implemented in modern graphics cards works perfectly. Note the exceptional performance of the GeForce 8800 in both resolutions. The Radeon X1950 XTX and GeForce 7950 GX2 keep the CPU load at about the same level and not higher than 50% in the 1080p resolution.

On the other hand, we use a clip with a rather low bit-rate, thus making the decoder’s job simpler. The load is going to be higher if a HD-DVD disc with H.264 video content is played because the bit-rate may be as high as 30Mbps then.

The only clip in the VC-1 format that we have at our disposal makes up for its resolution of 1280x720 pixels with a high frame rate and a bit-rate of 15Mbps. Thus, it is indeed a very hard test. The Avivo engine processes this file less efficiently than Nvidia’s PureVideo HD does, yet the results are acceptable since the CPU’s cores are each loaded by half only.

WMV HD is a rather simple format to decode and every premium-class product handles it with ease, keeping the CPU load below 25%. The Radeon X1950 XTX and GeForce 7950 GX2 are equals in the 1080p resolution, and the GeForce 8800 GTX has the best results.

So when it comes to highest-performance graphics cards available on the market, each of them has all the capabilities necessary to decode video of various formats, including HD content, and can take up most of the job even in the hardest case, allowing the CPU to be loaded by no more than 45-50%.

The average CPU load varies from 6% to 36% depending on the format, except for DVD and DivX SD.