Your computer is not digital cable ready

The following page is a general overview of options for recording digital cable in standard and high definition, primarily from a US perspective. It is not a how to guide, but instead is a jumping off point for those who are interested in building a MythTV system and recording digital cable.

General Overview

Recording digital cable versus analog cable should, in theory, be a simpler matter than recording its analog counterpart, due to the fact that unlike analog television, digital television need not undergo analog to digital conversion and encoding to be digitally stored on a computer. Instead, the digital stream is simply "downloaded" as is in the form of a transport stream. In practice, however, recording digital cable is more complex due to industry imposed encryption; cable companies often encrypt the channels provided via their cable service such that only rented set top boxes (or other means such as CableCARD) are capable of receiving and "descrambling" the channels for viewing.

To that end, two of the three options for recording digital cable solely depend on the encryption status of your cable service. These two options are to use a QAM tuner card to tune the digital channels or to use FireWire output from a cable company provided cable box, and they are the sole means of viewing digital cable channels in their unaltered digital form, as well as the only means to receive high definition television provided through digital cable. The only option that works regardless of encryption status is the analog tuner card option, but this method does not preserve the digital quality of the incoming video and hence can produce serious degradation of the quality of the video depending on a number of factors. Read on for a breakdown of these three options.

HD component

Hauppauge has released the Hauppauge HD-PVR, a high definition component capture box. The box is capable of encoding 480i, 480p, 720i, 720p, and 1080i component video into h.264 video with a hardware based encoder. It is fully supported in Linux, and can provide MythTV users a way to record all of their digital HD content with negligible quality loss, regardless of encryption status, when paired with a cable or satellite company provided tuner or STB. Judging by the mailing list, this has become one of the most popular options.

The Bottom Line: Necessary Equipment and Services

QAM tuner card

In the US, digital cable is generally transmitted via quadrature amplitude modulation or QAM, a means of transmitting digital data such as digital video streams. These streams, if unencrypted, can be tuned via a QAM tuner card. These cards simply "download" the digital video streams straight from the cable to your hard drive in their original form, hence preserving their original quality. They support both standard definition digital television and high definition digital television.

This method is the most reliable means of recording digital cable, assuming your QAM channels are not encrypted, as it does not rely on any outside hardware from the cable company which avoids the support problems of FireWire set top boxes as stated below. Unfortunately, QAM channels are almost always provided encrypted, so this method does not work for most. The only exception is the free to air (FTA) high definiton channels (such as ABC, CBS, NBC, etc..) that cable companies by law must provide in the clear, though that's hardly a consolation as these channels are provided for free over the air via the ATSC standard. Additionally, the native numbering system for QAM tuning differs from that of the lineup providers (see Adding Digital Cable Channels (For ATSC/QAM Tuner Cards - USA/Canada)

To check if your channels are provided in the clear via QAM, you must attempt to tune them either with a QAM tuner card in a PC, or with a newer television set that has a built in QAM tuner. Alternatively, you can contact your local cable company, but that may prove to be a frustrating experience. It's also important to note that cable companies can change their encryption status when they please, so while your channels may be unencrypted today they might not be tomorrow. This isn't too common, but it is possible and definitely something to be aware of. A third option is to check the channel lineups provided by Silicon Dust.

FireWire via set top box

Using FireWire, a set top box rented from the cable company is used to access your digital cable channels and then pass through the unencrypted digital video streams to your computer. This method also preserves the digital quality of the video streams, and it also has the added benefit of being able to work when the QAM channels are encrypted. In this case, the set top box essentially decrypts the video being provided by the cable company and then passes it to the computer in an unencrypted form via a FireWire interface. Myth either changes channels via the FireWire interface itself, or if that function is not supported on the set top box in question, an IR blaster can be used, and then the output from the FireWire is simply "downloaded" to your system in its original transport stream.

The problem is that in addition to QAM encryption, digital cable channels can also be encrypted such that they are not able to be passed through via the FireWire for non-Windows users. This is known as 5C encryption, and channels encrypted with it cannot be accessed via FireWire. 5C encryption varies by local franchise, and can often be seemingly quite random where some channels are encrypted but others are not without apparent reason, but some franchises such as some in the Seattle and Portland, OR areas provide nearly all of their channels without 5C encryption. At the very least it is much more common to have non 5C-encrypted channels than unencrypted QAM channels, so it is often the best way to record digital cable.

The downside is that using this method you must rely upon a rented piece of hardware from your cable company that may be subject to change. And because of the variety of cable boxes on the market, it is impossible to support all of them, and at this point Myth's FireWire support should be considered young. It works rock solid for some, but for many it is less then 100 percent reliable and can require considerable tweaking to get working in such a manner. This support is improving considerably with each release, however. Also, as cable companies are only required by law to provide cable boxes with FireWire output for high definition subscriptions, you may have to pay extra to get such a box as most companies charge extra for high definition enabled cable service.