ATI Universal Video Decoder vs. Nvidia PureVideo HD for H.264, VC-1

The newest generations of GPUs – ATI Radeon HD 2400/2600 and Nvidia GeForce 8600/8500 – have got more advanced video-processors than their predecessors, but the developers have taken different approaches here, just as they did in the other areas.

Decoding any video content is a multi-step process, so the resulting success depends on an efficient performance of each step on the hardware. The decoding of H.264 and VC-1 can be divided into four steps:

• Bitstream processing/Entropy decode
• Frequency transformation
• Pixel prediction
• Deblocking

The most resource-consuming are the first two steps that involve decoding data encoded with entropy algorithms like Context-Adaptive Variable Length Coding and Context-Adaptive Binary Arithmetic Coding, and performing inverse Discrete Cosine Transformation (iDCT). These have not been supported on the GPU until recently, but both GPU developers have introduced appropriate subunits into their new GPUs because these steps are calculated inefficiently on the CPU.

However, VC-1 uses entropy compression algorithms other than those used in H.264 and which are not supported by the current PureVideo HD processor of GeForce 8500/8600. The UVD can perform bitstream processing for both codecs, which is an advantage of Radeon HD 2400/2600 GPUs.

For today’s CPUs, bitstream processing shouldn’t be a big problem even with HD content, yet this technology may come in handy for mobile systems or systems with ultra-low power consumption.

We’ll now check out the CPU load as well as the video playback quality provided by different graphics cards.