iMovie imports footage into events. You then cut an event’s clips together in a project. Details of these events, projects and their clips are stored in the iMovie library file. By default this .imovielibrary file lives in your Mac’s Movies folder. If you use Time Machine to back up your Mac, it will also back up your iMovie library file to a separate hard drive, so you can use Time Machine to restore your iMovie library. However, as HD video takes up a lot of space, your Mac-based iMovie library file can be many gigabytes in size. We’ll show you how to create a new iMovie library on a separate drive. As well as storing new events (and their clips) in this new library, you can also move existing events to it. This gives you another way to back up events or free up space on your Mac’s hard drive.
1 Create a new library
Go to File>Open Library>New. In the Save window, browse to your external hard drive. Create a new folder. Label the new library ‘External Library.imovielibrary’. Click Save.
2 View the new library
Your new external library will appear in iMovie’s Libraries panel. At this stage it will contain no events, projects or video clips. It’ll just feature an empty event with the current date.
3 Import new clips
If you import clips from a camcorder or folder, they will be stored in the currently selected external library on your external hard drive. This stops them clogging up your Mac.
4 Copy or move events
To copy an old event from the original library to the new one, drag it to External Library. To move an old event so that it only exists in the new library, hold the Command key as you drag.