[AG-TECH] Quad Capture card performance

[Derek Piper]

	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 - dcpiper at indiana.edu - (812) 856 0111
IRI 323, School of Informatics
Indiana University, Bloomington, Indiana