Hello and welcome to the forum!
For your first post, you have provided scant information to even offer a guess, so please help us first: 1) What computer are you using (model/year); 2) What OS X is installed (I'm assuming you have a Mac); 3) What is the movie format(s) and are these 'legal' copies; and 4) Have you check the
MPlayerX Blog (there is a 1.1.0 version now) for a potential solution?
Now, I do not use that app so cannot speak from personal experience, but answers to these questions may help others better respond. Dave