iXBT Labs - Computer Hardware in Detail






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

March 21, 2006

Part 5: High Definition Video 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, especially in H.264 format (as a new version of MPEG4). This format provides that cherished video quality with maximum data compression.

Unfortunately, HD Video promotion currently includes only bashful attempts to give users a chance to watch movies on a large screen with fantastic resolution. CeBIT'2006 visitors could see demos in this format practically on each large display. But it's not quite correct to speak of the "HD format", because HD actually refers only to a video resolution and a frame rate. This video must be encoded with modern codecs, to squeeze this file into a disc. Of course, you may use good old MPEG2. But in order to provide adequate quality at such resolution, a high bitrate is required, which results in an increased data size. So usual DVD5 will accommodate only half an hour of HD video. That's why MPEG4-family codecs go to the forefront, including H.264 - they provide high quality at lower bitrates.

But nothing comes for free. Decoding High Definition MPEG4 (and MPEG2) heavily loads a processor. While Intel Celeron 2 GHz processor has no problems playing DVD, decoding HD Video is beyond its strength.

You can learn more details about HD Video in a separate article on our Digital Home web site.

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

It's generally known that decoding this video format heavily loads a processor. There were some cases when a 1080p movie 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)

  • Microsoft Windows XP
  • Windows Media Player 9 Series
  • DirectX 9.0
  • 3.0 GHz processor or equivalent
  • 512 MB of RAM
  • 128 MB video card
  • 1920 x 1440 screen resolution
  • 24-bit 96 kHz multichannel sound card
  • 5.1 surround speaker system"

Theoretically, all the latest cards support High Definition Video 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 the drivers, starting from Version 83.70, support the program interface for video decode acceleration (DXVA) for processors, published in the table at the link above.

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. 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 High Definition Video:

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 to enable hardware decoding of High Definition Video, along with installing Driver 83.70 or higher, you should find proper patches and versions of the above mentioned products and enable Hardware Acceleration in program settings.

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

  • Athlon 64 (939Socket) based computer
    • CPU: AMD Athlon 4000+ (2400MHz) (L2=1024K)
    • Motherboard: ASUS A8N32 SLI Deluxe on NVIDIA nForce4 SLI X16
    • RAM: 2 GB DDR SDRAM 400MHz (CAS (tCL)=2.5; RAS to CAS delay (tRCD)=3; Row Precharge (tRP)=3; tRAS=6)
    • HDD: WD Caviar SE WD1600JD 160GB SATA

  • GeForce 7800 GTX (reference, PCI-E, 512MB GDDR3, 550/1700 MHz)
  • RADEON X1900 XTX (reference, PCI-E, 512MB GDDR3, 650/1550 MHz (625/1450))
  • GeForce 7900 GTX (reference, PCI-E, 512MB GDDR3, 650/1600 MHz)
  • GeForce 7900 GT (reference, PCI-E, 256MB GDDR3, 450/1320 MHz)
  • GeForce 7600 GT (reference, PCI-E, 256MB GDDR3, 560/1400 MHz)
  • Operating system: Windows XP SP2 DirectX 9.0c
  • Monitors: ViewSonic P810 (21") and Mitsubishi Diamond Pro 2070sb (21").
  • ATI CATALYST 6.3; NVIDIA Drivers 84.20.

We played our test video fragment (video: WMV9 Pro 1440x1080 24 fps 8.38 Mbps; audio: WMA9 Pro 5.1 48 kHz 24 bit 384 kbps) in three modes using NVIDIA cards: with full hardware support for Windows Media High Definition 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 High Definition Video decoding more than the others). We also publish GeForce 7800 GTX results for comparison.



Efficiency of hardware acceleration for High Definition Video is evidently almost identical in the 7600 and 7800 cards. The results are evident. Note how different CPU loads are without hardware support for High Definition Video in PowerDVD and WMP . Considering that PureVideo decoder was uninstalled in all playback cases without High Definition Video 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 with disabled High Definition Video 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 X 1 xxx cards:

Note that we installed the trial version of ATI decoder. But it was practically no good. Results with enabled and disabled hardware support for High Definition Video 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. High Definition Video 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.

The High Definition Video 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, we can say that hardware support for High Definition Video in new products from NVIDIA 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 High Definition Video 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, but... The 256-bit X1800 GTO card is impending over it. We have already analyzed this battle in the $250 market segment in a separate article.

We can see that it will all depend on prices. The 7600 card has already appeared on sale (at the raised price of $275 on March 20; but we don't know prices for the X1800 GTO at the end of March, 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)

April 6, 2006

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