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From: "R. Lewis"
Subject: Re: Four (4) TV images on one computer monitor
Date: Sun, 17 Nov 2002 11:52:35 -0000
Organization: Nextra UK
References: <4PtB9.854$fY3.firstname.lastname@example.org> <1UBB9.5952$nK4.email@example.com>
NNTP-Posting-Date: Sun, 17 Nov 2002 11:51:38 +0000 (UTC)
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"Grahame Kelly" wrote in message
> firstname.lastname@example.org wrote:
> >> Do you know if there are any video capture boards that will allow us to
> >> capture four (4) TV shows at the same time?
> > I don't think so.
> > There shouldn't be a problem sticking 4 in, though the drivers may not
> > cope well. I know the linux BT848 drivers (the chip used in most low-end
> > capture cards) will cope with at least two cards, I don't think there
> > be a problem with more than two.
> > The resolution may be limited by the PCI bus bandwidth, you probably
> > do better than around 1024*768 total resolution, as the PCI bus can't
> > much more data than that.
> > But, 4 windows of 500*300 or so should be OK.
> I run 4 x PCI TV (BT484) type cards under Linux concurrently without any
> problem (read = As I require them to run to capture and detect the
> animals I am studying). One point to note is all the video capture cards
> MUST BE the same type and model to be supported by the driver. You cannot
> mix and match. Driver won't work correctly.
> That said, you will have problems with a 4 channel card (I have one) in
> to get 4 separate channel frames into one viewable picture size ( 4 x
> channels with each channel picture 256x192 pixels = 1024x768 - std. SVGA )
> the s/w driver has to switch between channels (say at 0.5 sec intervals)
> capture a frame BUT be aware that each channel Mux requires a
> time probably in the order of 5->10 frames [which equates on 50Hz System
> another 0.5 second] so you will only get each channel view
> updated every 1 second or so, sequentially not concurrently).
> There are commercially available PCI cards that have quad capture circuits
> that allow concurrentcy > 10fps viewing - BUT the viewing problem now is
> limited by the PCI bus speed, the type/style of AGP card (it its off the
> PCI bridge on the motherboard because you are viewing while capturing) and
> other factors. I have found that saving captured frames to disk, then
> a Linux tool like VLoopback and CamStream allows the best results by
> priority to the capture to disk process and then the viewing process.
> See: http://www.exploits.org/v4l/ for more on the subject.
> In my tests a 1GHz SMP (2 x PIII CPUs) performed poorly on a Gigabyte
> motherboard because the PCI bus and PCI bridge where unable to maintain
> throughput conditions controlling 4 video capture cards.Normally I had
> experencied on an older PentiumPro SMP system the best PCI throughput even
> though the PPro CPU was only 200MHz, beating hands-down the PIII SMP
> system. Goes to show motherboard design is major decider on performance -
> and it all depends on the applications to be run. On another system, a
> uniprocessor PIII/1Ghz Gigabyte motherboard, throughput was sustained.
> On another P4/1.5Ghz Apton motherboard throughput was less than PIII/1Ghz
> Gigabyte momo. So, its all up in the air unless you have the resources and
> time to test and select.
> My results - Every motherboard/PCI combination will have good and bad
> on sustained throughput. Best to go for (in order of priority):
> A. Fully PCI 2.2 compliant motherboard, 2.1 compliance is less effective.
> B: 66MHz or greater PCI bus clocking,
> C: PCI 2.2 compliant Quad Video Capture Card with onboard buffering
> D: A AGPx4 spec'd or better graphics card for viewing.
> E: Fast-SCSI III and/or Fast IDE2/66 drives on seperate controllers.
> F: Best speed memory SIMMS/DIMMS you can get to assure low memory
> G: S/W side, Drivers that allow double or triple frame buffering.
> Applications that make use of priority requests.
You must not assume that all quads operate in the same manner as the way you
anticipate the one that you have had operates.
They do not: 16 and 32 way splitters would be unusable if this were the
As I said before - get hold of a CCTV person/ company and they will be able
to tell you of the many options you have here.
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