Legacy media files are compatible with macOS Mojave, but they won't be with future macOS releases. Legacy media can include footage recorded with cameras like Flip Video cameras, footage from GoPro cameras recorded in the CineForm format, video files in the DivX format created with software, footage shot with many other older cameras, or files modified with older software.
While your Mac is running macOS Mojave, follow the steps in this article to back up your iMovie libraries, and complete and update projects that contain legacy media.
To make sure media you create now will be compatible with future macOS releases, use iMovie supported cameras.
Back up your iMovie library
Before completing projects, back up your iMovie library. You can store your iMovie library on an external storage device such as a USB drive, FireWire drive, or Thunderbolt drive formatted as APFS or MacOS Extended (Journaled).1 Don't store iMovie libraries on external storage devices like SD cards, USB flash drives, drives shared on a network, or an external drive or other disk used for Time Machine backups.
- To make sure all external media is collected inside a library, consolidate library media.
- Click on the Finder icon in the Dock, then choose Go > Home from the menu bar at the top of your screen.
- Open the Movies folder, then drag files named iMovie Library and iMovie Theater to your external hard drive.2
1 The APFS format is recommended for volumes using macOS 10.13 or later.
2 In most cases you have only one library, and it's located in the Movies folder. However, you might have more than one library, and you might have moved them to a different location on your Mac. Make sure to locate and back up all iMovie libraries.
Finish iMovie projects with legacy media
After you back up your library, finish editing any iMovie projects that have legacy media, then export them as QuickTime movies.
- To open the Projects view, choose Window > Go to Projects, or press 2.
- Select the project you want to export, click , then choose File.
- Click the Resolution pop-up menu, then choose the highest resolution setting.
- Click the Quality pop-up menu, then choose High.
- Click the Compression pop-up menu, then choose Better Quality.
- Note the estimated file size under the thumbnail. You'll need at least that much free space on the external drive you're using to back up the exported QuickTime movie.
- Click Next.
- Type a name for the project in the Save As field, navigate to the location where you want to save the file, then click Save.
- To back up the QuickTime movie, copy it to your external drive.
Update an exported project
If you want to update a project you've already exported as a QuickTime movie, create a new project, import the QuickTime movie, then add new clips at the beginning or end of the original clip. You can also add cutaway clips above the imported QuickTime file in the timeline to replace or update sections with new clips. To add completely new sections to the exported QuickTime movie, split the clip to add new clips in between.