How do I trash the iMovie Preferences File? and Why?

If you are having problems with iMovie, then at some point, someone may suggest that you trash the preferences file.

There are several things that can go wrong in iMovie.

• Your OSX may not be installed correctly. Solution: reinstall OSX. (Last resort)
• Your iMovie may not be installed correctly: Solution: reinstall iMovie. (Next to last resort.)
• You may have 3rd party components (like 3ivx or Perian for example) that are outdated and cause system crashes. Solution: Delete these components, or get updated components from the 3rd party.
• You can have a corruption in your Project file. Solution: Use Time Machine to go back to a working version of your project. But trash preferences first, because corrupted preferences may cause your restored project to become corrupted again.
• Apple may introduce bugs. Solution: Wait for Apple to fix, or use Time Machine to revert to a earlier version of the iMovie app.
• But sometimes, iMovie acts up, and it is specific to your user account. If you have another user account on the same Mac, iMovie works fine, but when you want to use iMovie with your user account, iMovie messes up. This is most likely a corrupted preference file called com.apple.iMovieApp.plist
• Also, sometimes iMovie will not see your iPhoto, or your Aperture, or your iTunes. This can also be fixed many times by trashing the preferences. In this case, look for a preferences file called com.apple.iApps.plist
• If trashing the iApps.plist file does not help you with iTunes or iPhoto or Aperture, see this thread for more ideas. https://discussions.apple.com/thread/2168081?start=0&tstart=0
  

Many times people will suggest that you trash your preferences because it is the easiest thing to do. You want to try all the easy stuff before re-installing OSX, for example.

1. If iMovie is still working, go to iMovie/Preferences and note your current preferences so you can easily re-enter them later.
2. To trash your preferences, close iMovie.
3. Then open the Finder.
4. Press CMD + SHIFT + G or, if you prefer, 'Go > Go to Folder' in the top menu.
5. Type: ~/Library/Preferences/ (Note: The Tilde ~ is on the uppercase position on the key to the left of the number 1 on your keyboard)
6. Press Go
7. Drag the com.apple.iMovieApp.plist file and/or the com.apple.iApps.plist file to the trash.
8. Next, empty the trash.
9. If you trashed the com.Apple.iApps.plist, then open iTunes, iPhoto, and Aperture so they are pointing at the library you wish to use in iMovie. (You can then close them.)
10. Finally, restart iMovie.
11. Remenber to go to iMovie/Preferences and re-enter your preferences. Be sure to enable the Advanced Tools.