Newbie Video Question (WMV)

I'm working on old video captures to put on you tube. As of right now I'm using Windows Movie Maker ( I know, its all I have right now).

So the way I'm editing is to take the mpg file from the capture and trim out what I don't need. Then if the resulting wmv file is longer than 15 minutes, I run it through again to split it in half.

My question is, is this degrading the quality of the video by running it through a 2nd time? Or is it ok to keep encoding wmv file without any loss of sound or video quality?