OTA / ATSC broadcast HDTV	ATSC tuner PCI or USB + UHF antenna + booster	Local HDTV networks, PBS-HD
Digital Cable: Clear QAM	QAM tuner PCI or USB	Music-only channels, MTV-HD, CNN, ESPN, Fox sports, etc.
Digital Cable: Encrypted QAM, no 5c	Cable Company-provided STB with working 1394 ports	Discovery HD, Food, ESPN-HD, Science, History, Bio, etc.
Digital Cable: Encrypted QAM, 5c-encrypted	Cable Company-provided STB + component video capture device	HBO, HBO-HD, certain TV shows on the major networks.

Software will be something like SageTV or MythTV.  These packages typically support 4 tuners or more.  SageTV will even treat the 1394-connected STB as a tuner.  We will attempt to create this monster of a machine.  The first three rows have been nearly perfected by many hardcore enthusiasts in forums out on webland.  But the fourth row above is most intriguing.  There is only one product as of mid-2008 which can capture up to 1080i, and is actually affordable:

This is the long-awaited, Hauppauge HD-PVR, available now for $249.
Click on the image above to go to their website

Let's hope it works, and works well enough that quality is not compromised.  Now all we have to do is figure out how to get everything to work together efficiently and easily.

As for capturing using 1394, there are numerous guides in various forums detailing the steps on how to install the set-top-box driver and recording on your PC.  Here is one of them:  http://replayguide.sourceforge.net/dct6412/ Our test STB is a Motorola DCH-3416, a DVR with dual tuners, a 160GB HDD, HD capabilities (HDMI and Component outputs), and two 6-pin 1394 ports.  It also has an eSATA, Ethernet and USB ports, but those are of little use to us now.  Note that the PC can only be 32-bit Windows XP.  Not too sure about Vista, but certain that 64-bit OSes are not supported by these drivers.

To see if a channel can be captured on your PC, a diagnostics page can be brought up by tuning to the desired channel, turning off the unit, then immediately pressing the OK button.  Select d06, and there information there will tell you all you need to know.  Reports from other users on other cable providers are conflicting, but for our test, this is our conclusion:

DRM:  0x00 means unencrypted QAM, 0x01 means encrypted QAM.  However, we've seen premium movie channels report this flag as 0x00. 
RC:      0x00 means you can record via 1394, anything else means you cannot
CCI:    On our test, we've seen both 0x00 and 0x02, and neither had an effect on the ability to record a program, whether it was a live stream, or a recorded show stored on the DVR.

Recording on the PC using CapDVHS is very simple.  A couple settings just need to be set on the last tab, select your save-to folder, and that's it.  Just select the 1394 capture device, then hit record.  Or, you can use it just like a VCR, and program the Timer Recordings on the first tab.  Here it is recording a clip from an HD channel at 1080i, 29.97fps:

Bit rate is a healthy 38Mbps, and because it is streaming form the STB, no caching of the data takes place.  Saving this to your HDD can be challenging to some PCs.  Choppy playback is usually a symptom of a slow disk subsystem.  In our tests, we recommend having a fast HDD separate from the boot HDD, one with a large cache (16MB or larger).  Otherwise, a RAID-0 or 5 array is recommended as the storage subsystem. 

Playing back the TS file is no problem at all in most media players, as long as a good CODEC bundle is installed to handle MPEG-2 and AC3 filtering.  Here is a screenshot of a captured HD program played back on the PC:

1080i (1920x1200 PNG)

Have fun capturing!