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23rd June 2005, 23:24 | #2 | Link | |
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24th June 2005, 09:27 | #4 | Link |
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Actually theoretically the 7800gtx could be very effectively programmed to help video encoding. Programmible shaders can be used to help encoding tasks for example fft3dgpu - an avisynth plugin. It uses directx9c shaders to "render" a powerful denoiser at high speed. It might not end up being all that useful for something like h.264 though - I really don't know\
-MiSfit
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24th June 2005, 09:37 | #5 | Link |
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the problem with GPU general purpose programming is that the download speed from the AGP (and even pci-express now) to the main memory is hella slow. Don't expect more than 30 or 40Mb/s... I'll let you do the math to have the maximum framerate you can achieve with this sort of bandwidth.
Btw, even with a fx5900 the processing power is interesting, it's just that nvidia and ati doesn't want you to use the gpu for something they don't want (what, you wouldn't pay a lot of $$ for their crap PureVideo system !). |
24th June 2005, 10:43 | #6 | Link |
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excuse my newbieness, but cant x264's already existing ability for multithreaded encoding making use of dualcore cpus be called "hardware accelerated encoding"?
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24th June 2005, 11:15 | #7 | Link | |
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Regards, -Lev |
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24th June 2005, 12:04 | #8 | Link |
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well, i was reading totally the contrary about pci-express at least... It can do 1.5GB/s but that doesn't mean that the gpu let you do it. I found a link somewhere (talking about fast memory move) the guy was getting 16Mb/s (!) from his 6800.
Well i would happily have more informations on how to achieve the speeds you're talking about. (iirc, the 40/50Mb/s value was what tsp got with his fftgpu avisynth plugin, at least at the begining, over AGP. the same, i'm interested by any information on how you got 200Mb/s ) |
24th June 2005, 12:26 | #9 | Link | |
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The sutiation could be much better, since the numbers are still far from theoretical peak (4 GB/s), but I have the feeling that the situation is improving. Regards, -Lev |
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24th June 2005, 18:38 | #11 | Link | |
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We're talking about a piece of dedicated circuitry that is built specifically for encoding x264 (or possibly other codecs). Or using a GPU to help accelerate the encoding process. |
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24th June 2005, 23:33 | #12 | Link |
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From what I know, using GPU shaders for ME and transforms should be possible but a big problem is that the GPU drivers "optimize" the shaders you send them.
The result can vary from speed improvement over inaccuracies to utter nonsense! If anyone knows a way to circumvent this optimization, please do tell. bis besser, Tobias
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25th June 2005, 06:09 | #13 | Link |
interlace this!
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aren't drivers something that can be fixed with a download? there's plenty of haxx0red drivers out there, but i'm not sure if shader optimisation is something that can be hacked (and if it can, what speeds would you end up with?).
it'd be really really really really good to see GPU/whatever accelerated encoding though. AFAIK some cards already "assist" in this kind of stuff, but that's mostly for decoding i think. it'd be good to be able to encode in faster than realtime (think of doing 2-pass in the time it takes to play out!). well, there's some clever people out there. i wish i had the maths and nunchuk skills to do it myself.
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27th June 2005, 09:27 | #14 | Link |
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OK, we know that the download speed is far from ideal according to some posts. But this is fine, because we only need something that will do about 4 times the bit-rate that you encode with. With x264 and many codecs, that is about 10 Mbits/sec. If the max bandwidth is 40 or 50 Mbits/sec, according to some reports, that's gonna be enough.
I can see a really big problem with this. Until the GPU speeds start coming anywhere near the CPU speeds, the GPU just physically cannot keep up with the pace of the CPU. As a result, the CPU encoding speed is throttled significantly to allow the GPU to keep up. So unless GPU speeds are going to magically hike to 3 GHz in the next 6 months, I rather think that we're out of options when it comes to encoding with the GPU.
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27th June 2005, 10:31 | #15 | Link | |
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Are you measuring speed or clock frequency here? They are NOT the same! And a third point: Your claim that a couply Mbit/s are enough download bandwith is only true if you do everything including bitstream encapsulation on the GPU. The current flexibility of the Shaders is not fit for this task. Therefore you have to download intermediate representations which are more bandwidth hungry and finish the encoding job on the CPU for the time being. bis besser, Tobias
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27th June 2005, 11:20 | #16 | Link | |
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The frequencies of GDDR3 can go as high as 1066 MHz, which is pretty fast. The RAMDACs are limited currently to about 400 MHz, which ain't bad. I'm confused, because the Northbridge can run at about 1 GHz. I know it affects CPU speed, but does it affect the speed that the graphics card runs at? Or is that left to the PCI-E controller?
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27th June 2005, 12:19 | #17 | Link | |
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Why are you so obsessed with clock frequencies? The important thing is work done per time unit. The parallelism of GPUs has been increased dramatically in the last few years (24 parallel shaders in the 7800GTX). If the used algorithms provide enough parallelism it is more efficient to design a chip at lower clock since the overhead due to the pipeline registers is lowered. Less overhead means less power at any given compute speed. What I'm trying to tell is this: compute speed = clock frequency * parallelism If you compare two CPUs which have the same amount of parallelism (like P2 and K6(-2) almost had) then the one with higher clock is faster. But once the parallelism is significantly different you have to take it into account. bis besser, Tobias
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27th June 2005, 13:46 | #18 | Link |
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Think about it... why do we need a graphics card: We need it to speed up graphics processing.
A CPU by itself cannot run a game at max res, max details with a good framerate (ignoring hardware directx issues). Yet a new GFX card can. Therefore it should be obvious that at graphics processing, an ATI/Nvidia card is much faster than a pentium/amd processor, even though they are clocked at a much much lower speed. |
27th June 2005, 15:12 | #19 | Link |
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a subtile difference : they are faster when executing code for what they have been designed ..... try to run some algorithm, like a collision detection, with a lot of branchements on a GPU (even though this is changing with the latest chips), and see....
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28th June 2005, 03:03 | #20 | Link |
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Noone has yet got hardware accelerated decoding working on the MS platform yet (which is a heck of a lot simpler):
My last post there gives reference to what Apple is doing, which uses OpenGL run by the GPU to process filters on images/video in realtime for both playback and editing. Next step is hardware assisted encoding. |
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