iMovie freezes upon deleting from the Project Media; how do I fix?

Whenever I try to delete any media from iMovie the spinning rainbow wheel appears and iMovie renders frozen. It's probably because of some corrupted file by which I'm trying to delete in the first place, so I go to the iMovie Library and try to delete the file there; but then I go back and when I try to delete something else it freezes as well. Now I don't know which file is corrupted and I've tried basically everything, restarting, force quitting and reopening, etc. How do I fix this?