Quit iMovie, copy the complete library to a supported external drive, and open the copied library before deleting the original. Move the library as one item. Picking apart its package in Finder makes it difficult to know whether every project still has the media it needs.
This is most useful when you want to keep editing older projects. If you only need the finished movie, an exported video and an editable library serve different purposes. Decide which you need before making room.
Prepare a suitable destination
Apple supports an external USB or Thunderbolt storage device formatted as APFS or Mac OS Extended (Journaled), and says not to use a device used for Time Machine backups. Its iMovie library migration guide also advises against SD cards, USB flash drives, and shared network storage for the library.
In Finder, use Get Info on the destination and the library to compare available capacity with the copy size. If the destination is the wrong format, do not erase it while it holds your only copy of other files. Choose another drive or back it up before changing the format.
Copy the complete library
- Back up your current work and quit iMovie.
- Open your home folder’s Movies folder in Finder. The default library is usually named iMovie Library; a custom library may be elsewhere.
- Copy the library to the external drive. Wait for Finder to finish.
- Double-click the copy on the external drive and allow removable-volume access if prompted.
- Open several projects and play clips from different events before removing the internal copy.
For a large archive, add an export check: share a short section of a representative project and review the resulting file. Include one project that uses older imported footage, since testing only your newest project leaves most of the archive unexamined.
Why two library copies still use space
A copy preserves the original. That is helpful during verification, but it means the internal disk will not recover the library’s space until you remove the old copy and empty the relevant Trash. Review the exact path first so you do not discard the SSD copy you just tested.
Do not interpret a smaller external library as a successful copy without investigation. Check that Finder finished and that you selected the intended source library. A duplicate name makes this mistake easy.
If iMovie opens an empty library
Apple notes that when the external library is unavailable, iMovie can create a new empty library in the Mac’s Movies folder. Reconnect the external drive and open its library directly. The empty window alone does not prove your projects have been deleted.
Before importing more footage, check which library is open. Otherwise, new clips can accumulate internally while older projects remain on the SSD. Give multiple libraries clear names that indicate their purpose, such as a year or project, rather than a series of indistinguishable copies.
Choose relocation or cleanup based on the goal
If you still need the full editing history, relocation is often a clearer decision than repeatedly clearing temporary files. If you want to reduce the archive itself, review iMovie events and library storage before deleting events. If storage still looks full after the move, use our post-deletion space checks.
Keep the external library backed up independently. Moving a single copy from one device to another changes where the work lives, not how many copies protect it.