After you make an archive (backup copy) of your camera’s contents on your computer or on an external hard disk, you can import the footage into iMovie from the archive.
To import video from an archive:
In iMovie, choose File > Import > Camera Archive.
The File menu appears in a light gray bar across the top of your computer screen.
In the Finder window, navigate to the folder of the archive you want to import, and then click Import.
Follow the instructions for importing video from a camcorder: Import video from a USB camcorder or camera.