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Programmable Video-processor

The home PC has long been advertised as a universal entertainment center, so the developers don’t have to divide processors for personal computers into categories basing on their typical application. The entire series of chips is usually endowed with the most copious bundle of features.

The NV40 has a programmable video-processor intended for encoding/decoding video streams and performing various operations on them. You may have heard S3 talking about such things with regard to their DeltaChrome chip. ATI’s RADEON 9500/9600/9700/9800 chips can decode video using their pixel processors, too. The video-processor of the NV40 features:

  • Support of adaptive de-interlacing;
  • High-quality scaling and filtering;
  • Removal of blocky artifacts;
  • Integrated TV-coder;
  • Inverse telecine (3:2 pulldown);
  • Conversion of color spaces;
  • Conversion of the refresh rate;
  • Gamma correction;
  • Noise cancellation;
  • Processor amplifier;
  • HDTV support (720p, 1080i, 480p, CGMS modes are supported);
  • Hardware synchronization of audio and video streams;
  • Support of MPEG-1/2/4 encoding/decoding;
  • Support of WMV9H.264 decoding.

In fact, this video processor is a full-fledged processing device capable of performing scalar and vector calculations as well as executing branches.

The video processor doesn’t seem to be an independent functional unit. It is more likely that the pixel processor of the NV40 bears the load of processing video. This is our supposition, though, as NVIDIA haven’t yet clarified the situation.

As for the efficiency of the NV40’s video processor, NVIDIA claims it takes 60% and more of workload at encoding video into the MPEG-2 format and up to 95% at decoding MPEG-2.

That’s not the only application of the video processor. Its programmable architecture makes it possible to lay special effects onto the picture in real time. Until now, only S3 Graphics with its DeltaChrome could boast this capability.

We think the most useful and interesting functions of the video processor in the NV40 core include hardware MPEG-2/4 encoding, MPEG-4 and WMV9 decoding, and support of HDTV. HDTV is the most resources-hungry format today: modern CPUs and graphics cards have no problems decoding DVD movies (MPEG-2), while the decoding of a HDTV stream may be difficult even for a very fast CPU. Hardware support of MPEG-4 (DivX and XviD) looks promising, too, since this format is widespread today. Again, NVIDIA claims its video processor to be flexible and programmable. In other words, the company can increase the number of supported formats in the future by simply revising the drivers.

Like in our S3 DeltaChrome review, we decided to try the NV40 at decoding MPEG-2/4 and HDTV – we don’t like to rely on the manufacturer’s words only. For the latter format, we used the same video clips as with the DeltaChrome, written in the HDTV WMV format. Alas, our testing ended without really starting out. When trying to play any video with BSPlayer, we saw a blank gray window, although with sound. It turned out that the NV40 with the current version of its drivers didn’t support the Overlay Mixer mode. The problem disappeared when we switched to the VMR-9 mode, but only to be followed by another. When playing a HDTV WMV video clip with Windows Media Player 9, we had the central processor loaded to the full 100%, and the video went on convulsively, although the image quality was all right.

The CPU workload was much high above NVIDIA’s claims during MPEG-4 playback, too. All the time a 640x480 video clip encoded with the DivX codec was running, the central processor was loaded by 60-65%, which is too much for such a video file. For comparison, the RADEON 9800 XT played the same clip, loading the system by 35-40% only.

DVD playback was all right, save for the same too-high CPU load: about 30% in both WinDVD and in Windows Media Player.

These results make us think that the current version of the ForceWare driver has the support of NVIDIA’s video processor disabled. The developers may have encountered problems with this unit and put it off for a while to avoid stability issues. This is unlikely to be a hardware problem, since video processing seems to be performed by the ordinary ALUs and if the ALUs were defective, the entire NV40 core wouldn’t function properly. One way or another, the promised video-stream-processing capabilities of the NV40 remain on paper so far.

Anyway, we hope that this is a temporary situation and the new ForceWare version will come with the video processor support. If it does, we’ll surely test it and evaluate it as it deserves.

 
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