My pleasure. I had this problem with iMovie for months, I couldn't think of anything I did that would have changed the OS environment so drastically that would corrupt the most basic function of iMovie (i.e., save the movie file!), and I couldn't find anywhere near as elegant of an app (and as affordable) as iMovie to manage simple file editing and I was starting to get panicky (I couldn't find a player/editor that can save movies in reverse playback and that is essential to my application).
I read so many different ways to attempt to get around this silly problem;
- start up in Safe Mode to reset certain files and then reboot,
- reinstall the OS,
- upgrade to 10.15,
- hack iTunes mobiledevice utility (which will likely interfere with IOS backups and syncing of newer model iPhones, by the way),
- type a few lines of code into Terminal.app...
...the list goes on and on.
What ended up working is the simplest solution: throw out iMovie and reload it fresh from the App Store!
Worked like a charm, for me at least, running High Sierra on a 27" iMac. And I was surprised this version of iMovie (10.1.12) was still available at the App Store because Apple stopped officially supporting High Sierra this past September!
