CPU vs GPU - whats more important for HTPC video quality?

[merovingian]

I think the GPU is more important than the CPU for picture quality. But I think the quality of the source material is more important than both of them.

Seriously, I think the real value of the GPU can only be assessed when throwing natively interlaced material at it. Despite the hushed tones used to describe 1080p24 as the holy grail, native 1080i50 and 1080i60 is probably the most computationally intensive material you can throw at your GPU. Motion-adaptive or pixel-adaptive deinterlacing of this material is a non-trivial exercise. And my understanding (which is not backed by direct comparisons and experience on my part) is that the quality of the deinterlacing is dependent on the quality and capacity of the GPU. And, especially, the number of shaders.

FWIW, I have an 8500T, and I think it's performance on natively interlaced material, be it HD or SD, is less than spectacular. I have never tried a superior card, whilst holding all other variables constant, so I can't say with any certainty that a superior GPU will improve the performance. However, the experience of others who have done these comparisons (see avsforum.com) is that there is a difference.

I also find that the limitations of the 8500GT deinterlacing are insignificant compared to the compression artifacts present in the source material (which brings me back to the opening point of my post). For example, HD AFL on Ten is perhaps one of the best tests for HD picture quality and deinterlacing you can perform on your system, because it is natively 1080i50 and features a lot of fast motion, but I find that the macroblocking artifacts are far greater in number, and far more distracting, than deinterlacing artifacts. So while it may be possible to improve the PQ by upgrading my GPU, I don't think the cost-benefit analysis really stacks up. Particularly since the bulk of what I watch is 1080p hidden inside a 1080i signal - ie. not natively interlaced. That all said, the next time I upgrade, I will get a 9600GT (or better).

[arkay]

But again the GPU can only be more important to PQ ONLY IF the software running on the GPU is better than the software that would use the CPU to perform the same task.

i.e. Adaptive de-interlacing of 1080i content is certainly time consuming and processor intensive but an upgrade in GPU is only going to aid in doing it if the video decoder (the software putting together the image) is written to make use of the GPU as a processor for that purpose.

Obviously there is a lot that goes into putting together the image. Colour space conversion, de-interlacing, scaling, the actual mpeg and/or H.264 decompression, motion compensation etc etc.. There's no end to the amount you can massage a video stream prior to display. But it matters 2 parts of bugger all if the GPU is not being used to do it because the decoder you are using is not specific to that GPU.

In the case of Vista the vast majority use the bundled decoders and not purevideo (or avivo in ati land). For them there is no gain to be made from upgrading to the latest 9x00 series card, as much as Nvidia would like you to believe there is.

Also, if the majority of video you watch is coming from ffdshow (i.e. non mpeg/live TV or DVD), then the CPU is responsible for ALL your video processing, except scaling the image for final display. So there is no gain to be made from more expensive video cards for ffdshow playback. The api's used by avivo and purevideo are not published and are not available to anyone without hefty licensing fees. Only software such as the purevideo decoders or products such as PDVD (that are licensed) can make use of the power the gfx card may have.

I think the CPU is more important than the GPU for the reason that the CPU is the component capable of processing video data for all streams where the GPU is responsible only in very specific and tailored instances.

Ultimately I guess you need the best of both to get the best video from all sources but at least know WHY you're upgrading video hardware before you do it. It's senseless to go out and spend $200+ on a new video card if you do not intend to use codecs and/or software that support GPU decoding on that card in order to make use of it.

It's wrong that cards are marketed as "having PQ benefits" whilst the small print (if you can find it or bother to look for it) reads "only when used in conjunction with software player abc for formats 123 & 456"...

Cheers,

Arkay.

[merovingian]

Originally Posted by arkay

i.e. Adaptive de-interlacing of 1080i content is certainly time consuming and processor intensive but an upgrade in GPU is only going to aid in doing it if the video decoder (the software putting together the image) is written to make use of the GPU as a processor for that purpose.

Obviously there is a lot that goes into putting together the image. Colour space conversion, de-interlacing, scaling, the actual mpeg and/or H.264 decompression, motion compensation etc etc.. There's no end to the amount you can massage a video stream prior to display. But it matters 2 parts of bugger all if the GPU is not being used to do it because the decoder you are using is not specific to that GPU.

In the case of Vista the vast majority use the bundled decoders and not purevideo (or avivo in ati land). For them there is no gain to be made from upgrading to the latest 9x00 series card, as much as Nvidia would like you to believe there is.

No doubt the GPU is pointless if it's not being used. Hard to argue otherwise.

However, regarding Vista and decoders - the Purevideo software decoder is irrelevant for Vista and PureVideoHD cards. PureVideo HD does not require the Purevideo software decoder. You need only the card, the Forceware driver, and a player/decoder that makes use of DXVA2.0. Vista's built-in MPEG2 decoder fits the bill. See here:

http://in.nzone.com/object/nzone_pvhd_faq_in.htm#Q6

[vlad]

Originally Posted by arkay

Ultimately I guess you need the best of both to get the best video from all sources but at least know WHY you're upgrading video hardware before you do it. It's senseless to go out and spend $200+ on a new video card if you do not intend to use codecs and/or software that support GPU decoding on that card in order to make use of it.

Arkay,
That was one of the reasons I am staying with MCE 2005. My decoder is PDVD7 and PQ is better than with MS decoder on Vista. In fact PQ is much better with 9600 GT than with my old 1600 Pro.
As for ffdshow, yes there is a limit on how much you can improve PQ of 360 Mb xvid.

[arkay]

Originally Posted by merovingian

No doubt the GPU is pointless if it's not being used. Hard to argue otherwise.

However, regarding Vista and decoders - the Purevideo software decoder is irrelevant for Vista and PureVideoHD cards. PureVideo HD does not require the Purevideo software decoder. You need only the card, the Forceware driver, and a player/decoder that makes use of DXVA2.0. Vista's built-in MPEG2 decoder fits the bill. See here:

http://in.nzone.com/object/nzone_pvhd_faq_in.htm#Q6

Fair enough. I'll admit to not having looked into it for a while. That being said though it's still only useful as a generic lowest common denominator DXVA implementation and from the perspective of trying to get the most in PQ the PureVideo HD codec is likely required.

I'm in 2 minds about it to be honest. On one hand it's nice to think that all that power on a GPU is being put to good use but likewise I'm not going to spend a lot on GFX's cards when my CPU is happy to bare the load instead. At least with a core2duo and an 8500GT I'm pretty much covered either way

Cheers,

Arkay.

[nikko1974]

Originally Posted by arkay

Also, if the majority of video you watch is coming from ffdshow (i.e. non mpeg/live TV or DVD), then the CPU is responsible for ALL your video processing, except scaling the image for final display. So there is no gain to be made from more expensive video cards for ffdshow playback.

I think the CPU is more important than the GPU for the reason that the CPU is the component capable of processing video data for all streams where the GPU is responsible only in very specific and tailored instances.

Excellent reply - AS ALWAYS Arkay.

This definitely fits me to a tee - my uTorrent & dedicated downlaod box are running 24/7....so short of standard FTA material thats my most watched content.

Does anyone know IF the cache of the CPU is of much benefit for HTPC tasks - specifically video related?

I can't imagine from what I've read it would - I mean with converting it from MPEG-2 to H264 etc - sure but I don't think for normal use its going to really do that much.

[merovingian]

Originally Posted by arkay

Fair enough. I'll admit to not having looked into it for a while. That being said though it's still only useful as a generic lowest common denominator DXVA implementation and from the perspective of trying to get the most in PQ the PureVideo HD codec is likely required.

Just to be clear, the Purevideo codec is not designed to be used with PureVideoHD cards under Vista. PureVideoHD is a silicon implementation in the GPU, not a software codec, and there is no complementary or necessary Purevideo software that goes with it. You just need a player that can use DXVA2.0 to offload to the GPU. (Where "just" is not necessarily a fait-accompli as you rightly pointed out earlier.)

Originally Posted by arkay

I'm in 2 minds about it to be honest. On one hand it's nice to think that all that power on a GPU is being put to good use but likewise I'm not going to spend a lot on GFX's cards when my CPU is happy to bare the load instead. At least with a core2duo and an 8500GT I'm pretty much covered either way

I think your skepticism is healthy. I think it's clear that the majority of the GPU power is targeted at gaming. And, as you said, the GPU is not being used at all for most users with most downloaded content.

As you may have seen around here before, I am personally no big fan of most downloaded BT content, and most of my viewing is broadcast MPEG2, usually 1080i (either natively interlaced or progressive-segmented-frames). If Nvidia and MS are both telling the truth, then my GPU is doing the work for this content.

Part of the difficulty is that you will be hard pressed to find any reviews that focus on the PQ performance of graphics cards. They're all crappy performance benchmarks for games, performance benchmarks for CPU offloading, or very dry HQV ratings. There's just nothing there to help the videophiles get the best picture. Seeing with your own eyes is the only way to know.

When a 1080i50 HD AFL Bluray is eventually released, free as it will be of the macroblocking compression artifacts that plague the broadcasts, I will definitely get my hands on it. And a 9600GT. And compare the performance of the 9600GT versus the 8500GT, to see whether I got any value for money.

[arkay]

It always infuriates me when I go looking for video card reviews and it's benchmark after benchmark of 3D gaming performance with a one liner at the end "BTW, the card is fanless, great for HTPC use"... and that's all you get

It's a pity that matrox don't take on the HTPC crowd. They always made the best 2D PQ cards and they could focus on video PQ as they have no interest in gaming. It's sad but we're a niche market that had to use hardware from a much larger market who'd primary concern is not video playback...

I agree that for your preferred media type it's likely that you would benefit from the higher end card. Just wanted to make the point that it's a horses for courses thing for the benefit of most people (particularly new HTPC users). I hate to see people swept into hardware purchase for little or no gain.

Cheers,

Arkay.

[Jaiidan]

Hey guys

Just a little note on an upgrade I carried out today. I did have a 7600GS card in my rig and just upgraded it to a 8500GT.

With the 7600 card in my cpu usage was around 50% when Recording one HD FTA Channel and watching another at the same time.
With the 8500 Card in my cpu usage has dropped to around 20% for the same test

Cheers

J