Question about recording broadcasts on comcast's cable service.

A lot depends on your cable box outputs and Computer inputs. What are your in/out options? What kind of quality are you hoping for? What happens when you hook the cable directly to the tuner input on your computer -- do you currently have a tuner card installed? Comcast is shifting a lot of channels to spectrum locations that will require a special tuner or cable-card to tune in, if they are using standard channels your odds increase for easily doing what you want. If you have AV outs on the cable box you can get a simple AV input card for your computer and should be able to do what you want.

In order to get a lossless (from the cable box to your PC) capture you'll almost certainly need a cable card tuner, ie a Hauppauge WinTV-DCR-2650 or Ceton InfiniTV. Then you need to hope that Comcast has that channel set to "copy freely". Then, theoretically yes you could burn a Bluray disc (why you would want to with magnetic storage being so cheap, I don't know).

There are also some cards out there that will record anything from component inputs, then re-compress the video to h.264. That's lossy, but still HD. Cheaper cards that take composite video, will not be HD. Digital (without cable card) tuner cards will only be able to record OTA or in some cases clear QAM, but its very unlikely the channel you want to record is available on clear QAM. Unless you want to record NBA games on ABC.