What Format for Movies to Play Via MediaShare

I have 7 HD DVR's in my home and I have them all Networked and working wonderfully.  I have a Windows Home Server that my DVR's MediaShare see, and I have a rather large Collection of Movies on DVD that I would like to convert and store on my WHS to play through my HD DVR's via Media Share.... But what I don't know is the exact format of the MPEG2 Files for them to work on my DVR.  Does anyone know specifically what format I should convert the Media to?  Thank You for any help.