I used to use MythTV. I even built a PC with a device that could pull video from a cable box. There’s an IR blaster that will change channels on the cable box,

I used to use MythTV. I even built a PC with a device that could pull video from a cable box. There’s an IR blaster that will change channels on the cable box, and then a little box that takes the component video from the cable box (no DRM on that) and encodes it (to MPEG-2 if I remember?) MythTV will process the shows to flag commercial breaks, which you can then skip automatically. MythTV looks like it’s still an active project. I stopped using it because I just don’t watch much TV these days and I just got tired of maintaining it. Renting the DVR from Comcast is worth it to me for my meagre needs. But if you’re into TV and don’t mind some geekery, MythTV is definitely a powerful and flexible system.