Lost iMovie Footage!

The Library and Projects are completely separate from the iMovie app.

Are you saying that the iMovie app is damaged or missing?

If so, just re-download it from the App Store.

You could also try deleting the preferences which should be done whenever iMovie starts misbehaving.

 Hold down the  Cmd and Option keys as you launch  iMovie and this window will appear.

Click “Delete Preferences” and  iMovie will open in the default (as-new) mode with sometimes no projects etc. on the interface. 

If your project doesn’t load automatically you will have to navigate to it and reopen it.  Your project libraries by default are stored in your Movies folder unless you have specified somewhere different.

Was the backed up library not in the backups folder, or were you unable to find the backups folder?

To get to the iMovie Backups folder, follow this file path from the Finder menu:

Go/Home/Library/Containers/com.apple.iMovieApp/Data/Library/Caches/iMovieBackups

When you get there you will see a list of previous backups of your iMovie library.  Click on one dated just before your issue started.  iMovie will open in that library.   Navigate to your projects browser (where your projects are displayed as icons) and see if your projects are intact.

-- Rich

Have you tried double-clicking the Library to open it in iMovie? What happens?