How to capture security camera's video output

If I want to build a board to capture video signal from a security camera, what is the easiest approach? My understanding is an analog camera requires a capture card like function on the board involving adc, dsp, and dac.. I don't want to go that route.

I think a digital camera (or IP camera? are they the same) has onboard encoding chips so that its output is already digital and encoded. So can I just build a board that simply data-logs the incoming video stream onto an onboard harddrive? Do I need to add any data conversion function?

Are there such camera that outputs storage-ready signals?

Thanks for your input!!