Media Center records live television using the "dvr-ms" format - which is fine for playback on the Media Center PC, but not, for example, on my iBook G4. Here's how to convert it to a more pervasive format.

The dvr-ms format, according to the Microsoft description of it, "allows the creation of key PVR functionality, including time-shifting, live pause, and simultaneous record and playback".  It also allows for the inclusion of digital-rights-management functionality:

The ability to access *.dvr-ms files by using DirectShow depends on the copy protection policy set by the content owner and/or broadcaster. Microsoft Windows XP Media Center determines the copy protection policy by reading the broadcaster's copy protection flag (CGMS-A). If the content owner and/or broadcaster has set the policy to protect the content, playback will be restricted to the Media Center PC used to record the content.

...which is an unfortunate indication of things to come.  You can play dvr-ms files on other XP systems, BTW, by installing Q810243 - Windows XP SP1 Update: Watch TV Shows Recorded by Media Center PCs on Other Windows XP PCs.

On non-XP systems (like my iBook), however, you can convert dvr-ms to wmv (Windows Media Video) using an excellent tool called DVR2WMV, which you can get here, and which is mirrored here in case you can't connect to the first link.  Basically, this tool will look in the folder Media Center uses for recorded video, and allow you to convert it to wmv format.

The resulting, converted files can be played in Windows Media Player including, happily, Windows Media Player 9 for Mac OS X.

Here are some stats for conversion of a 15 second clip:

Original file size: 14mb
Time to convert: 50s
Converted file size: 3.43mb
Converted file size (Pocket PC format): 690kb

If you're interested in the quality, you can download the normally converted file here (3.43mb) and the same clip converted for Pocket PC here (690kb)