The Great Avivo/PureVideo HD Showdown



As bombshells go, the stunning announcement by Warner Brothers at this year's CES that the studio was dropping its support for HD DVD in favor of Blu-ray has to rank among the biggest. The studio had formerly released movies in both formats and the decision to go exclusively Blu-ray cast a pallor over the HD DVD booth at the annual consumer electronics Mecca. It seems that the news have also had quite an instant impact in the marketplace, with reports that sales of Blu-ray players had seen a dramatic increase in the week following the announcement, with a corresponding fall for HD DVD players.

So by all reckoning, whether the media or consumers, the format war has reached a decisive turning point in favor of Blu-ray. For those who have been waiting on the sidelines for the stalemate to end, there is now just one viable choice (though there are probably plenty of discounted HD DVD players and media for bargain hunters). While there are those who feel that we'll be eventually getting our movies through digital downloads, it doesn't seem the case yet in the near future. Hence, it's an appropriate time to examine the state of HD video playback now and compare the two major PC hardware solutions to HD video decoding available now, ATI's Avivo HD and NVIDIA's PureVideo HD. Although image quality is another crucial factor in choosing your hardware, we have seen other reviews showing both to score rather similarly in benchmarks like HQV and hence we won't be covering this aspect today.

The State of Avivo HD and PureVideo HD

In our previous series of articles on this topic, we had discussed what is required to get HD movies playing on the PC and the performance impact of having hardware acceleration with the appropriate graphics cards. Since then, both the leading graphics chipmakers, ATI and NVIDIA have made significant changes to their hardware in order to reduce the decoding workload on the CPU. First up, we have ATI and its Avivo technology, now branded Avivo HD to distinguish its HD capabilities. If you're feeling lost about what hardware accelerated HD video decoding is all about, we recommend that you browse through our earlier articles first.

Previously, we had looked at ATI's Radeon X1000 series and seen how Avivo was implemented in those graphics cards. To recap briefly what was mentioned before, the hardware present was not involved in all the stages of decoding. Specifically, the entropy decode step was not done by the video processor but instead left to the CPU. Since the entropy algorithms used for HD formats like H.264/AVC and VC-1 can be quite complex and processor intensive, this naturally results in higher CPU utilization. The CPU overhead is no doubt lower than a similar system without hardware acceleration but as we have seen, 60 - 75% CPU overhead leaves much room for improvement.

This has been remedied with Avivo HD, which now includes a Universal Video Decoder (UVD) that includes entropy decoding as part of its workload, thus freeing up your CPU. It is implemented with dedicated hardware within the GPU and works independently of it. Additionally, post processing of HD video is now done by an Avivo Video Post Processor (AVP) that alleviates the amount of work done by the GPU's rendering pipeline for tasks like deinterlacing, gamma correction and upscaling/downscaling. In short, even the low-end GPU will have no issues handling HD video decoding, which was not always the case for earlier Avivo implementations. According to ATI, their Avivo HD is obviously the superior solution and the image below illustrates their competitive edge over NVIDIA's PureVideo HD.

According to ATI and illustrated by this diagram, it's Universal Video Decoder has the edge over its rival when it comes to VC-1 decoding. We'll see in our testing if that's true in reality.

So what exactly is NVIDIA's PureVideo HD? The evolution of the company's technology from the original PureVideo to PureVideo HD has not been entirely smooth, with some developments that could be confusing to consumers. Initially introduced with the GeForce 6 series, PureVideo was quite limited in terms of its HD capabilities, with relatively weak hardware acceleration for HD formats. Then came PureVideo HD which has a dedicated video processor known as VP1 that is found on the GeForce 7 series and then on the older G80 based GeForce 8 cards like the GeForce 8800 GTX. This is the same hardware that we discussed and tested in our previous article on HD decoding performance and where your decoding mileage could vary depending on the clock speed of the GPU.

With the introduction of the mid-range GeForce 8 cards, NVIDIA debuted its new version of PureVideo HD in the form of VP2. This new hardware adds more functionality to VP1 and takes up a larger share of the decoding process. For instance, for H.264/AVC decoding, VP2 is now capable of entropy decoding and inverse transform, making it a complete solution similar to ATI's Avivo HD. There is also an integrated bitstream processor that handles the entropy algorithms. Of course, while this combination is a significant improvement over VP1, it's not perfect since this applies only to H.264. For VC-1 decoding, the entropy decoding step is still reliant on the CPU. VC-1 decoding is nowhere as taxing as H.264/AVC decoding and that's one reason why NVIDIA hasn't actually taken the step to fully offload all stages of processing. In any case, we'll soon show you how both ATI and NVIDIA's solutions pan out in real usage.

Summarizing why you should get a VP2 equipped NVIDIA graphics card for your HD playback needs. This is the evolution of PureVideo technology from GeForce 6 to the current GeForce 8 series (excluding G80 based GeForce 8 cards).

Nevertheless, the addition of VP2 on all GeForce 8 cards excluding G80 based ones reinforces the HD decoding prowess of its graphics cards and NVIDIA has followed up by including this on the newer G92 products like the GeForce 8800 GT and the GeForce 8800 GTS 512MB SKU. The upcoming GeForce 9 series is also expected to have additional PureVideo HD features to lessen the demands on the CPU even further but that's for another day. As for now, we'll be putting both technologies to the test and see how they impact on CPU utilization for H.264, VC-1 and MPEG-2 decoding. We'll also be addressing some of the related queries that appeared while conducting our Avivo HD and PureVideo HD comparisons.