Just one (many) problem(s)

The app is great and everything but the problem is that I cant make a video longer then like one minute without it like bugging ! For instance, when I try adding text, the project doesnt show, and sometimes the sound fx wont resize and when I play the project, the screen turns black for a split second between each of the clips, and its really inconvenient. Plz fix and Ill rate five starzž$ ßØ¡iÎ1 !!!!!

LittleLeonard24 about iMovie, v2.2.3