MY Desktop computer is also my DVR as I have a tuner card.
I use Windows Media Center to do my recording, but these files are only playable on the specific desktop they were recorded by.
HOWEVER there is a program MCEbuddy that will convert these files to the fileformat of your choice automatically.
The program is Free but they encourage "Donations"
The current version (released December 22 2012) is 2.3.11
2.3.12 is available as beta currently
I have MCEbuddy set to covert to mp4 in a "new conversions" directory on another physical drive.