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Thinness rules!
0.09 Calibre, a Volley from California:
NVIDIA GeForce 7900 GTX/GT (G71),
GeForce 7600 GT (G73)

Part 5: H.264 Support

High Definition Video

As we have already mentioned, one of the new features of GeForce 7600-7900 cards is hardware support for decoding high definition video (high resolution), especially in H.264 format (as a new version of MPEG4). This format provides excellent video quality with maximum data compression.

Unfortunately, H.264 promotion currently includes only bashful attempts to give users a chance to watch movies on a large screen with fantastic resolution. Even at CeBIT'2006, which has just ended, visitors could see mostly demos in this format. Even those movies, advertised as high definition, were actually shown in usual DVD format (MPEG2), that is in regular resolution.

But tomorrow is certainly with such excellent movies (I don't mean content, of course, just video quality :).

It's well known that decoding video of this format heavily loads a processor. There were some cases when a 1080p movie was played too slow on a rather powerful CPU, if a video card took no part in the process (except for demonstrating ready video data). For example, here you can see the recommended system configuration for Windows Media High Definition Video:

Optimum Configuration (Play 1080p video with 5.1 surround sound)

Theoretically, all the latest models support H.264 decoding. You can see a more detailed list of GPUs that can process video here.

Of course, along with GPU support, sterling operation of the above mentioned components also requires software support (drivers and applications). All drivers, starting from Version 83.70, support H.264 for the processors, listed in the above table.

But that's not enough, you also need a decoder to work with various multimedia players. NVIDIA developed its own PureVideo Decoder for players without their own decoders (now it works not only with MPEG2, but also with other formats). It's a shareware product with 30-day trial, after which you should buy the decoder on the NVIDIA web site.

You should configure the decoder for sterling H.264 operation:

I repeat that this product is necessary only for WMP-like players or small free programs that do not have their own decoders. Such popular players as PowerDVD, WinDVD have their own engines, so this decode feature must be integrated into the suite. So, in order to enable hardware decoding for H.264, along with installing drivers 83.70 or higher, you should also find proper patches and versions of the above mentioned products.

Thus, we have come to the most interesting point: the actual decode process. Here is the testbed configuration:

We played the test movie in three modes on NVIDIA cards: with fully enabled hardware support for H.264 in PowerDVD; with disabled hardware support; and without PureVideo Decoder in WMP. Considering that all three new products demonstrated nearly identical results, the diagram contains the results of GeForce 7600 GT (I guess this product needs hardware support for H.264 decoding more than the others). We also publish GeForce 7800 GTX results for comparison.

Results >>>

Efficiency of H.264 hardware decoding is nearly identical in the 7600 and 7800 cards. The results are evident. Note how different CPU loads are without hardware support for H.264 in PowerDVD and WMP. Considering that PureVideo decoder was uninstalled in all playback cases without H.264 hardware support, it becomes clear that purely software decoding is done only in case of WMP, while PowerDVD certainly uses some video card's capacities even without H.264 hardware support. Or these players are just too different in implementation.

We publish the following diagram for you to compare how the same technique works on ATI RADEON X1xxx cards:

Results >>>

Note that we installed the trial version of ATI decoder. But it was practically no good. Results with enabled and disabled hardware support for H.264 are nearly identical. We were told that ATI was well informed about the problem of the new decoder running on AMD processors. This problem is being solved now. The company promises to release a new version of the decoder soon, which will offer a more noticeable effect. By the way, on the whole we can see that CPU is loaded less by ATI cards than by NVIDIA cards. It's up to a driver here. H.264 support (partial) is implemented by Canadians a tad better. But it's hard to tell whose fault it is: better GPU instructions or the driver.

And in conclusion I want to note that the H.264 load on all cards under review did not raise the core temperature much, so there is no point in publishing monitoring results.

Quality issues.

We noticed no problems with ATI cards, but the 7800 card sometimes displayed squares in the corners:


So, in a first approximation we can say that the hardware support for H.264 in new NVIDIA products has come up to our expectations. But there are some messages in forums from owners of the 7800 and 6600 cards that they do not get what is promised, even though this technique must work with these chips. Perhaps they just have a wrongly configured decoder, or they use PowerDVD/WinDVD without proper H.264 patches, which is more likely.

Our preliminary conclusions on GeForce 7600 GT have turned into final ones: it's a good product from all angles. Yep, the 256-bit X1800 GTO card is impending over it. We shall analyze this battle in the $250 market segment in a separate article.

As for now, we can see that the 7600 card has appeared on sale (at the raised price of $275 on March 20; but we don't know prices for the X1800 GTO after March 22, when the cards appear on the market), meaning that it already has some advantage over the competitor (an early bird catches the worm :) ).

Andrey Vorobiev (anvakams@ixbt.com)

March, 2006

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