Is there such a thing as a third party DVR that works with cable?

[EllisDee]

I’m reading about how to set up a computer as a dvr. In all of them, they say:

First, attach your cable connection or satellite cable to the video capture card’s input.

No set top box is mentioned. But isn’t the set top box required in order to unscramble the signal for premium channels like HBO? I’m so confused.