From: Michel L. <wa...@zo...> - 2002-06-26 21:12:48
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On Wed, Jun 26, 2002 at 11:24:18AM +0200, Arpi wrote: > Why are they against iDCT so much? Do they really think that people > will rip dvds by sniffing the PCI bus for idct samples??? I have to say I did not understand that part of Mark's message as well. It does not seem to make much sense (like, the decoder app should decode the IDCT coefficients to a nice array, and then the XvMC driver encrypts that array before sending it to the PCI bus ? Why would someone want to snoop it on the PCI bus if we already have it unencrypted in memory in the first place). But heh, if this is what the CSS licensing says, I guess we have to take it as a fact wether it makes sense or not. > Anyway, without iDCT what's the benefit of XvMC ? > I mean, you still have to do idct by software, and transfer the yuv image to > the card, through the very slow bus, the only benefit is doing MC by > hardware. Imho it won't speed up things at all, just makes things more > complex. The slow part of mpeg decoding is iDCT (this is the reason why is > sorenson so fast compared to mpegs - there is no idct just table lookup) > and transferring the frame to the card. On a celeron 366, 40% cpu is > required to dvd decoding, 55% for blitting. On x86, MC is about 30% of decoding time, IDCT is 25%, parsing of IDCT coefficients is 25%, and the remaining 20% are split up between everything else. (The numbers might have changed a bit since I last measured them, and I think the 20% for everything else might be closer to 15% now, but I havent double checked). So, XvMC without the IDCT might still save 30% of the decoding time - still, it's a smaller gain that what we could have if Xv images could be DMA'ed to screen instead of transferred by the CPU in the X driver code. (Xv display is currently more expensive than the total decoding time) So, I think XvMC support would be nice conceptually, but I wont get too excited about it until I have free drivers that can provide it. Cheers, -- Michel "Walken" LESPINASSE Is this the best that god can do ? Then I'm not impressed. |