how watch and record video from multiple webcam cameras on raspberry pi at the same time [duplicate]

I want to watch and record video from multiple webcam cameras on raspberry pi at the same time. How I use OpenCV library file?Which software I use?And I wanna put webcam cameras away 20 feet from sever raspberry pi board.It ok?And I wanna transmit video to network.. I am now studying Raspberry pi,so guide me please.

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