I've recently upgraded 11.10 to 12.04 and then reinstalled Pitivi and Gstreamer codecs ecxept the extra codecs and regardless of which container,vid codec or aud codec the rendering bar wouldn't move any help would be helpful, and if your wondering if it used to work in 11.10 it only work in the first few tries before it also stopped rendering.
P.S: I'm still a nooby.