Media Center and Digital Cable

I've been asked by quite a few people lately about how Media Center works with Digital Cable (particularly in respect to High Definition). While I don't at all mind fielding these questions, I don't think that I'm the best subject matter expert, since I don't have HDTV at home, and don't use Media Center in conjunction with my cable converter box.

But, I'll attempt to capture my responses here (hopefully it will be more concise than my off-the-cuff babbling that some of you had to suffer through).

First off, let's understand what's coming into your house on that coax cable. Unless your local cable company does something radically different than mine, then you should have a range of channels that are analog. That is, you can plug the coax into a regular television, and be able to tune to these channels. Note that the channel numbers might be different from what you would use on your converter box, but the point is that these lower channel numbers are not digital.

Your local network television affiliates are included in this range of analog channels, as is the Weather Channel, several home shopping networks, and the usual "Basic Cable" stations. For Media Center, a regular television tuner card, like the Hauppauge PVR-150MCE, works nicely, and can tune in these channels directly from the coax without needing your converter box.

Now, what if your local network affiliate simulcasts both analog and digital (ATSC) signals, as most stations in the USA are doing? This is outside of my domain of expertise, but I would guess that the digital portion of the broadcast might be included along with the analog signal, the same as it is over the airwaves. So, for instance, if your local CBS is channel 11, then perhaps you would be able to plug your coax right into your television (or separate tuner), change to channel 11, and then get the 16x9 ATSC picture instead of the old 4x3 NTSC picture. I welcome comments on this.

At the moment, Media Center only supports Terrestrial (off-the-air) HDTV. That is, you can buy a ATSC capture card, like the DVICO FusionHDTV5, that will tune in the same local digital signals that you can normally tune in on your television. If these signals are indeed available right off of the coax, then you again don't need the cable converter to record shows using Media Center.

So, where does that digital cable box come into the picture? Well, all of the digital cable channels that you cannot receive on the coax using a standard television are actually being "broadcast" on the coax as encrypted MPEG-2 streams. You can fit so many more digital streams into the same bandwidth as an analog channel, so this is what makes it possible to cram hundreds of channels into the same bandwidth as maybe 20 regular channels would occupy.

Let's say that you want to watch the Science Channel. Your cable box will actually receive the decryption keys from the head-end (assuming that you are authorized to receive the channel), and then will decrypt the signal and reassemble the video. Where it goes from here depends on your setup, but somehow, the video comes out of the converter box as a signal that your television can use.

In order to record these "digital only" channels on Media Center, you need to receive the signals coming out of the converter box (in effect, your Media Center becomes the television in the above description).

Using a cable converter introduces a few issues:

1. How does Media Center change the channel in order to record a show? This is usually done using an IR blaster. Your Media Center remote control probably has a blaster built into the USB device that you thought was just a receiver. What you have to do is RTFM and figure out how to program the blaster. Then, Media Center will have the ability to emulate your converter box's remote control, and change the channel. The caveat here: Media Center has no idea about the state of your converter box; it is just blindly trying to change the channel. If the converter is powered off, then you're not going to record your show.

2. What about different TV Guides for direct-cable versus through-the-converter-box (since the channel numbers might be different between the two)? At this time, the standard response is that Media Center only supports one Electronic Programming Guide (EPG) at a time. You need to choose to use Media Center only with your cable box, or only with direct coax, but not a combination. However, for the homebrew PVR builders: Other PVR software, like GBPVR, etc, will allow you to have different EPGs tied to each tuner card, if you need it.

3. Can I tune in the digital-only channels without a converter box? Nope. Remember that these MPEG-2 streams are encrypted, so the tuner needs to communicate with the headend in order to get the decryption keys. However, there will be a type of tuner coming out in the near future called a Cable Card. This is essentially a converter box built into a PCI card. However, the homebrew PVR builder will not be able to use these, because the DRM folks are requiring that a converter card be certified for use with a complete system, and the certification process costs $10,000 per attempt. The end result is that you'll have to buy a complete Media Center PC from one of the big system builders (Dell, HP, Gateway, etc) if you need Cable Card support.

That just about sums up what I've been telling people lately. Please feel free to comment on your own experiences to support or refute anything that I've stated here.