Problem – iMovie constantly fills hard drive space

You may find that when editing in iMovie – even without bringing in any new clips – your hard drive starts to fill up. When you check what’s eating at the storage (Apple Menu | About This Mac | Storage | Manage…), you find that the iMovie Library is taking up way more space than the videos you put there in the first place.

You’ll remember that iMovie for macOS makes a copy of every video file you import. This means that when you’re considering storage requirements for your project, you need to double up: a 20 GB video file will ultimately take up as much as 40 GB on your Mac when you start editing with it. But this isn’t what continually fills up space on your Mac. What does is the creation of render files.

Render files make it easier to play your timeline without things juddering to a halt. This rendering process is iMovie doing some export work while you’re editing...