How can I copy/cut/paste with quicktime pro if those commands are greyed out in the Edit menu?

Yes, I have quicktime pro, not regular qt. And sometimes the edit menu commands appear, but sometimes they're greyed out and not usable. I don't know if this has to do with the clipboard or what. I can move the cursors in a movie to select a small portion of the movie, but when I go to copy that portion, it doesn't work.