I don’t know whether it’s safe or not, but I deleted them anyway. That seemed to solve the problem for awhile, but I’ve been seeing it again. I’ve been working on this project for two years (nearly 300 GB of video), and after all this time, my media has all gotten quite complicated. I’m thinking of deleting ALL of it and recapturing only what I’m going to use AND in a more systematic way. Best of luck to you.