I have two MP4 files that I generated with Camtasia Studio. I need to join them together post rendering with Camtasia (it can't be done during the Camtasia rendering process). Looking for a utility or technique that will work to join these, preferably that doesn't require re-rendering all the video again.
Update: Either Windows (preferred) or Mac. Doesn't need a GUI if it is a good command-line app.