The New Face of PureVideo HD

The processing requirements of the highest quality HD-DVD and Blu-ray content are non-trivial. Current midrange CPUs struggle to keep up without assistance and older hardware simply cannot perform the task adequately. AMD and NVIDIA have been stepping in with GPU assisted video decode acceleration. With G84, NVIDIA takes this to another level moving well beyond simply accelerating bits and pieces of the process.

The new PureVideo hardware, VP2, is capable of offloading the entire decode process for HD-DVD and Blu-ray movies. With NVIDIA saying that 100% of the H.264 video decode process can be offloaded at up to 40 Mbits/sec on mainstream hardware, the average user will now be able to enjoy HD content on their PC (when prices on HD-DVD and Blu-ray drives fall, of course). There will still be some CPU involvement in the process, as the player will still need to run, AACS does have some overhead, and the CPU is responsible for I/O management.

This is quite a large change, even from the previous version of PureVideo. One of the most processing intensive tasks is decoding the entropy encoded bitstream. Entropy encoding is a method of coding that creates variable length symbols where the size of the symbol is inversely proportional to the probability of encountering it. In other words, patterns that occur often will be represented by short symbols when encoded while less probable patterns will get larger symbols. NVIDIA's BSP (bitstream processor) handles this.



Just adding the decoding of CABAC and CAVLC bitstreams (the two types of entropy encoding supported by H.264) would have helped quite a bit, but G84 also accelerates the inverse transform step. After the bitstream is processed, the data must go through an inverse transform to recover the video stream which then must have motion compensation and deblocking performed on it. This is a bit of an over simplification, but 100% of the process is 100% no matter how we slice it. Here's a look at the breakdown and how CPU involvement has changed between VP1 and VP2.



We have a copy of WinDVD that supports the new hardware acceleration and we are planning a follow up article to investigate real world impact of this change. As we mentioned, in spite of the fact that all video decoding is accelerated on the GPU, other tasks like I/O must be handled by the CPU. We are also interested in finding videos of more than 40 Mbit/sec to try and push the capabilities of the hardware and see what happens. We are interested in discovering the cheapest, slowest processor that can effectively play back full bandwidth HD content when paired with G84 hardware.

It is important to emphasize the fact that HDCP is supported over dual-link DVI, allowing 8600 and 8500 hardware to play HDCP protected content at its full resolution on any monitor capable of displaying 1920x1080. Pairing one of these cards with a Dell 30" monitor might not make sense for gamers, but for those who need maximal 2D desktop space and video playback, the 8600 GT or GTS would be a terrific option.

While it would be nice to have this hardware in NVIDIA's higher end offerings, this technology arguably makes more sense in mainstream parts. High end, expensive graphics cards are usually paired with high end expensive CPUs and lots of RAM. The decode assistance that these higher end cards offer is more than enough to enable a high end CPU to handle the hardest hitting HD videos. With mainstream graphics hardware providing a huge amount of decode assistance, the lower end CPUs that people pair with this hardware will benefit greatly.

Under the Hood of G84 The Cards and The Test
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  • poohbear - Tuesday, April 17, 2007 - link

    sweet review on new tech! thanks for the bar graphs this time! good to know my 512mb x1900xtx still kicks mainstream butt.:) Reply
  • tuteja1986 - Tuesday, April 17, 2007 - link

    Total disapointment :( ... Could even beat up a X1950pro. They really need to sell at $150 otherwise you would be better off buying a X1950GT or 7900GS for $150 to $160. At the current $200 to $230 price you could get a X1950XT 256MB which could destroy it but that GPU needs a good powersupply. Only thing going for a 7600GT is the DX10 support and Full H.264 , VLC , Mepg 4 support but that can be found on even other cards. Reply
  • Staples - Tuesday, April 17, 2007 - link

    I have been waiting several months for these cards and boy and I disappointed. I figured this month I would get a new PC since April 22 the prices of C2D also drop. My idea was to get a C2D600 and an 8600GTS but after their lack luster performance, my only option is an 8800GTS which is $50+ more. Not a huge difference but I am very compelled to wait until the refresh comes out and then maybe I can get a better deal. I really hate this senario where ATI is down, AMD is down and no competition is leading to high prices and crappy performance.

    Hopefully in another 6 months, AMD will be up to par on both their processors and CPUs. I will be holding on to my current system until then. I found it disappointing that these cards do not come with 512MB of memory but their performance is actually even more disappointing.
    Reply
  • JarredWalton - Tuesday, April 17, 2007 - link

    Well, the R6xx stuff from AMD should be out soon, so that's going to be the real determining factor. Hopefully the drivers do well (in Vista as well as XP), and as the conclusion states NVIDIA has certainly left the door open for AMD to take the lead. Preliminary reports surfacing around the 'net show that R600 looks very promising on the high end, and features and specs on the midrange parts look promising as well. GDDR4 could offer more bandwidth making the 128-bit bus feasible on the upper midrange parts as well. Should be interesting, so let's see if AMD can capitalize on NVIDIA's current shortcomings.... Reply
  • PrinceGaz - Tuesday, April 17, 2007 - link

    It might be a good idea to read more reviews before writing off the 8600 range.

    Over at , they found the 8600GTS easily beats the X1950Pro and even though the models they tested were factory overclocked, one of them had only a 5% core overclock and no memory overclock and was still well ahead of the X1950Pro. At worst the two cards were roughly even but in many tests the 8600GTS (with just 5% core o/c) was considerably faster. As say in the article link
    quote:

    New GeForce 8600 GTS Shines
    If you have been waiting for a DX10 video card capable of playing today's games, your wait is over. The GeForce 8600 GTS series GPU destroys ATI's current X1950 series for right around $220.


    So who do you believe? I guess I'll need to read several more reviews to see what's really going on.
    Reply
  • Spanki - Tuesday, April 17, 2007 - link

    I agree that that review it paints a different picture, but I have no reason to disbelieve it. I mean, they do their testing differently (try to find the best playable settings for each card), but it is what it is... I mean, the tables show the differences in the cards, at those (varrying settings) and so they therefore draw the conclusions they draw, based on that (with card X, I can enable option Y at these frame rates, but not on card Z - at least at the same resolutions). It's not like they tried to hide the settings they used or the frame-rates they got with each set-up. I found it an interesting perspective. ~shrug~

    Anyway, my personal opinion is that they neutered this chipset too much. There looks to be a substantial gap between 7900/8600 and 8800 level performance and the sweet-spot for this price-point would have been right in the middle of that gap... maybe they're planning a 8700 series chipset?
    Reply
  • Griswold - Tuesday, April 17, 2007 - link

    Thats a funny review. I'll stick to the other 90% that say this fish smells. Reply
  • GoatMonkey - Tuesday, April 17, 2007 - link

    Reply
  • yacoub - Tuesday, April 17, 2007 - link

    HardOCP's review disagrees with almost everyone else's results and also reads like a marketing advertisement for the product. I wouldn't give their review the time of day. Reply
  • PrinceGaz - Wednesday, April 18, 2007 - link

    They're normally very good which after reading HardOCP's review immediately after AT (whose I read first), I thought I should mention that not everyone found the 8600GTS to be slower than the X1950Pro.

    However, after reading several more reviews on other usually reliable websites, the consensus seems to be that the 8600GTS is well behind the X1950Pro, which does make HardOCP's finding seem very odd.

    I get the feeling that we're going to have to wait until nVidia get their drivers for this card sorted out as I suspect they are not all they could be, which they will hopefully have done by the time the HD2xxx series are launched, then the 8600/8500 cards can be retested and compared with their true competition.
    Reply

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