Thanx a lot Derek!! That was enlightening!!
----- Original Message ----- From: "Derek Piper" <dcpi...@indiana.edu> To: "John Hodrien" <jo...@comp.leeds.ac.uk> Cc: "ag-tech" <ag-t...@mcs.anl.gov>; "Natalia Costas Lago" <nata...@cesga.es> Sent: Monday, April 25, 2005 3:29 PM Subject: Re: [AG-TECH] Quad Capture card performance > > Of course if the system you're installing on only supports 32-bit x 33Mhz > slots (as many do) then you're not going to get a lot of benefit. Natalia, > what are the hardware specs on the capture machine you're upgrading or > rebuilding? > It's important to note too that however many PCI *slots* you have, you > (normally) only have one PCI *bus*. And the TOTAL bandwidth of that bus is > 32bit x 33Mhz = 132MBytes/sec. So however the cards are arranged (singly > or quad) you're going to run into that same bandwidth limitation. Of > course the quad capture card might be slightly more efficient due to it > being the only card on the bus and thus eliminating bus contention between > the capture cards. > To reiterate the math here? > > 33000000 x 32 = 1056000000 bits/sec PCI max > > = 132000000 bytes/sec PCI max > > 1 frame (24 bit color) = (768 x 576 x 24 / 8 ) = 1327104 bytes > > 25 fps = 33177600 bytes/sec > > x 2 captures = 66355200 bytes/sec > > x 3 captures = 99532800 bytes/sec > > x 4 captures = 132710400 bytes/sec > > Derek > > John Hodrien wrote: >> On Mon, 25 Apr 2005, Natalia Costas Lago wrote: >> >>> >>> We are about to purchase a Spectra8 capture card or Winnov Videum 4400. >>> It's >>> a very good point not to have to use 4 PCI buses, that's what I like >>> most of >>> both cards, however I am concerned to performance issues, I mean, a PCI >>> bus >>> allows 132 Mbps more or less, and the Spectra8 delivers 4 videostreams >>> at >>> 30fps 768x576 (it can be less, that's the worst case) (similar values >>> for >>> the Videum 4400 card). So, it seems to me that the PCI bus cannot >>> transmit >>> so much information, that means, does it drop frames? Maybe I cant get >>> the >>> highest resolution at 30fps (25fps for the Winnov card)?. >> >> >> It won't be 30fps at 768x576 will it? That's PAL resolution at NTSC >> frame >> rates. If you drop that to 25fps, the back of my envelope looks like >> you'd >> indeed be rather close to 32 bit PCI limits. The 4400 supports 64bit >> PCI, >> thus solving that problem. >> >> jh >> > > -- > Derek Piper - dcpi...@indiana.edu - (812) 856 0111 > IRI 323, School of Informatics > Indiana University, Bloomington, Indiana >
