ati capture API

[aoehlke]

hello all. I'm a sage user, but this question I have is not really sage related.
In my day job, while I'm not watching my sage PVR, I am a software developer.
Our company has been contracted to do some video imaging work and we are using a special form factor, (PMC) PCI video card with I believe an ATI radeon 9000 chipset(maybe 9600 not sure).

One of the tasks is to capture full frames of 1280x1024x32bit image data from the video card input and blend them or overlay them into/onto another image of similar size and color depth, that the video card is rendering already. I was passed a document today that showed the API into the ATI capture interface and it looks like it can support 30fps at that resolution. BUT... I dont think the PCI bus can support that bandwidth! by my calculation, the bandwidth required is 5megabytes per frame, by 30 fps is ~ 157 megabytes per second... the pci bus that the card is on, can only pass 133mbytes/s. that's not enough, and worse still, there are other cards and things on the bus.

So what I was wondering is... is there any way that I could get around not having to pass the captured image back to the motherboard for overlay? (ie leave it in video ram and then draw it over top before drawing it to screen?)
that way it never has to come off the PCI bus, it never even leaves the vide card memory ... it doesnt need to be processed... just overlaid.

seems like a weird place to ask such a question... but my bets are someone here has some ideas.