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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  • deathwalker - Wednesday, April 18, 2007 - link

    So, whats the word on the Ultra version of the 8600? Has that fallen to the wayside? Reply
  • crystal clear - Wednesday, April 18, 2007 - link

    Interview: NVIDIA's Keita Iida
    The future of Direct X, Crysis and PS3 under the spotlight.

    Keita Iida, Director of Content Management at NVIDIA sat down with IGN AU to discuss all things Direct X 10 and the evolution of their Geforce graphics cards. Iida goes into detail on the differences between developing for the PS3's RSX graphics processor, and the latest development tools to hit the scene.


    quote:
    Selected portions of the interview-


    IGN AU: What are your thoughts on Microsoft effectively forcing gamers to upgrade to Vista in order to run Direct X 10 - when there's no real reason why it can't run on Windows XP?

    Keita Iida: It's a business and marketing decision.

    IGN AU: Can you comment on what happened with NVIDIA's Vista drivers? You guys have had access to Vista for years to build drivers and at the launch of Vista there were no drivers. The ones that are out now are still basically crippled. Why did this happen?

    Keita Iida: On a high level, we had to prioritise. In our case, we have DX9, DX10, multiple APIs, Vista and XP - the driver models are completely different, and the DX9 and 10 drivers are completely different. Then you have single- and multi-card SLI - there are many variables to consider. Given that we were so far ahead with DX10 hardware, we've had to make sure that the drivers, although not necessarily available to a wide degree, or not stable, were good enough from a development standpoint.

    If you compare our situation to our competitor's, we have double the variables to consider when we write the drivers; they have much more time to optimise and make sure their drivers work well on their DX10 hardware when it comes out. We've had to balance our priorities between making sure we have proper DX10 feature-supported drivers to facilitate development of DX10 content, but also make sure that the end user will have a good experience on Vista. To some degree, I think that we may have underestimated how many resources were necessary to have a stable Vista driver off the bat. I can assure you and your readers that our first priority right now is not performance, not anything else; it's stability and all the features supported on Vista.

    IGN AU: So what kind of timeline are we looking at until the end user can be comfortable with Vista drivers? With DX9 drivers that work as stably and quickly as they do with XP?

    Keita Iida: We're ramping up the frequency of our Vista driver releases. Users will probably understand that we release a number of beta drivers on our site, so we're making incremental progress. We believe that, in a very short time we will have addressed the vast majority, if not all of the issues. We've had teams who were working on other projects who have mobilised to make sure that as quickly as possible we have the drivers fixed. I'm not going to give you an exact timeframe, but it's going to be very soon. We're disappointed that we couldn't do it right off the bat, but we hear what everyone is saying and we're willing to fix it.

    http://pc.ign.com/articles/780/780314p1.html">http://pc.ign.com/articles/780/780314p1.html
    Reply
  • xpose - Tuesday, April 17, 2007 - link

    This next gen purevideo stuff sounds amazing. I thought I was gonna have to get a new motherboard and dual core cpu to play some HD-DVD content smoothly. Please, do try and rush testing the purevideo stuff ASAP. Blu-ray and hd-dvd is growing. . . Reply
  • shabby - Tuesday, April 17, 2007 - link

    128bit/256meg for $200 bucks? Gimme a break. Reply
  • Sunrise089 - Tuesday, April 17, 2007 - link

    Unless these cards are majically fast under DX10 (and we all know they won't be, they will play Crysis, but not quickly) they offer less performance than even midrange parts from the last get.

    Anyone remember how a 6600GT offreed 9800pro beating performance, and how nVidia sold millions of them. I don't see that happening here. What I do see is a wait-and-see attitude. Does anyone else think it's VERY suspicious that there are no 64 shader cards? Here is what may happen: nVidia waits for the midrange AMD cards to emerge. If they offer better performance, nVidia slashes prices of these and releases a 8800GS with 64 shaders for $200. I won't be surprised at all if that's what we have in 3 months.
    Reply
  • JarredWalton - Tuesday, April 17, 2007 - link

    We've got 128 SP on the GTX, 96 on the GTS... and then 32 on the G84. I'd say there's definitely room for 64 SP from NVIDIA, and possibly 48 SP as well. Will they go that route, though? Unless they've already been working on it, doing a new chip will cost quite a bit of time and effort. I was expecting 8600 to be 64 SP and 8300 to be 32 SP before we had any details, but then the 8600 probably would have been too close to the 8800. Reply
  • kilkennycat - Tuesday, April 17, 2007 - link

    Er, wait (not too long) for nVidia's re-roll of the 8xxx-series on 65nm... You might just get your wish. I believe that nV is copying Intel's 'tic-toc' process strategy - architecture and go to production on a mature process (80nm half-node), then transfer and refine the implementation on the new process. Note the interesting and important tweaks in the implementation of the 8600 vs 8800... which gives a glimpse of the future 65nm 9xxx(??)-family architecture but with higher numbers of stream-processors and high-precision math processing for the expected GPGPU applications.

    nVidia has already hinted that the successor to the 8800 will be available before the end of 2007, and no doubt will be on 65nm for the obvious cost and yield reasons. If the R600 turns out to be a true contender for the 8800 "crown" in the same price-range, then I fully expect nV to accelerate the appearance of the 8800 successor. No doubt the design was started long before the 8800 itself was production-available.
    Reply
  • Toebot - Tuesday, April 17, 2007 - link

    No, nothing to sneeze at, just something to blow my nose on! Utter wretch. This card is NVidia's attempt to milk the Vista market, nothing more. Reply
  • DerekWilson - Tuesday, April 17, 2007 - link

    We should at least wait and see what DX10 performance looks like first. Reply
  • AdamK47 - Tuesday, April 17, 2007 - link

    With what software? Reply

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