How does a capture card work?

A capture card receives an input signal, and makes it available to you via capture software. For instance in my HTPC, I have 3 capture cards to manage my cable TV. From the wall, I split my cable steam into 3 wires, those three wires go to the input of my three capture cards. Windows 7 media center handles the input feed of the capture cards. I am left with a home made DVR that is faster, more configurable. You can use your capture card to capture just about video feed. For instance, you can run your camcorder output into the capture card and convert your old camcorder videos to computer content. There is a variety of capture software you can use to do the job.