[PiTiVi] change mkv file to something smaller a windows user can use

     I'm running PiTiVi 0.15 on Kubuntu 11.04 and using the method 
described at 
https://lists.ubuntu.com/archives/ubuntu-users/2011-November/254419.html 
to create an audio/video screencast of a presentation.  This results in 
a very large 151359-final.mkv file.  I opened it with PiTiVi and was 
able to render it to a smaller mp4 file on the second attempt.  The 
first attempt resulted in a file with no video but I changed the video 
codec to xvid for the second attempt.

     At any rate, what is the best way, including codecs and such, to 
change the mkv file to something smaller that a windows user will be 
able to use without having to install anything extra?  The audio is just 
me speaking.  The video is a pretty simple LibreOffice Impress 
slideshow.  The total time is around 45 minutes.

Jason
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