I use a video editor - specifically Adobe Premiere Elements 3.0. This is of course very definitely not Open Source. The same job can be done with a bit more difficulty with
http://www.virtualdub.org/ which was originally developed for that purpose, but has expanded into other fields. I think you'll have to get all the frames the right size and shape and bolt them all together in the application, then get your output codec from elsewhere - I tend to use Windows Media 720p, but there are DivX versions which are OS.