How do you hook up a new comcast cable box?

How do I hook up a Nintendo 64 to a Comcast High Def. Digital Cable box with a DVR?

• I have an old Nintendo 64 and I want to hook it up to to my home theater system. I have all the components running through a receiver but I do not have any RCA inputs left. Therefore, I am trying to run the Nintendo 64 through the above mentioned digital cable box, which has RCA inputs on the front and I can switch the signal by pressing the TV/VCR button on the cable box remote. The problem is that when I switch the system on I only hear the audio, the screen is completely blacked out. I can hear the game playing properly and I've tried swapping out every piece of the Nintendo 64 to ensure that the video game system wasn't the problem. Does anyone know what I'm doing wrong here? If you need more details I'm more than happy to provide.

• Answer:

  You don't. You use separate inputs on your TV or you get an Audio Video AB switch so you can choose between the two. For TVs without video inputs use a RF modulator and an antenna switch.