Record video on hard drive possible?

I have an underwater camera that is connected to a screen via a 20 m cable. Now the question is, is it possible to connect the screen to a laptop and then save the recordings directly to an external hard drive with a suitable program?

It depends on the type of signal that is transmitted from the cable to the monitor. An mp4 or avi signal could easily be recorded by a pc with a video capture program, provided that the cable can be disconnected from the monitor.

Assuming the camera is connected via HDMI, an ordinary HDMI capture card can be used to record the signal. Elgato, Blackmagic or Avermedia have a lot to offer.