Chosen Solution
I tried to perform a TimeMachine backup using a new external Seagate HD. It seemed the external HD was faulty. I sent it back and ordered a new one but that one also caused problems. Since then my iMovie keeps crashing all the time eventhough I never had problems with it before. Also my MacBook randomly crashed during the day which it never does. I just ordered a new external HD because I want to backup all my files ASAP if there is an issue with my hardware now. Do you have any ideas what caused this crash issue?
I would recommend you run OS Recovery. Restart your system and hold the Command & R keys and Run Disk Utility and then re-install the OS. References: About macOS RecoveryStartup key combinations for Mac Update (10/03/2017) Reinstalling the OS won’t effect your apps or data. I suspect you have OS corruption, this is the least aggressive action. If it fails to alter things we may need to wipe the drive and reinstall everything at that point we would first need to get a backup somehow. Given your problem I would then recommend finding a friend who has a Mac that you can connect your system to using Target Disk Mode. For now lets hope the simplest fix fixes things.
My iMovie started doing the same thing on multiple computers. It must be from a recent update. I crash when trying to edit or output a movie. The original media files came from a Canon DV camera.
