Video capture of multiple cameras

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• Is there any limitation on number of cameras that can be used?

an average usb2 controller can barely handle the throughput of a single hd webcam. so, already with 2 cams, you have to connect one to the front port, and the other to the back. (or reduce the resolution significantly). connecting 20 cams to a single machine like this is an illusion.

• are there any specification for type of cameras to use or any camera would work in video capture?

i got no idea, usually anything off-the-shelf should work. but i'd recommend to look for ip-cams, not usb ones, to overcome the problem mentioned above. you will still have network / cpu / gpu bottlenecks, connections will be laggy and time out, but it's probably the only way.

• I want to understand how cameras are indexed as 0,1,2.. in video capture. and how do i identify cameras based on index? because i need to define specific properties for each camera based on its location.

it's simply the order you plug them in.

• are these indexes always same for each camera even when application is restarted?

unless you change the physical order (plug in, plug out), - yes.