How to Import iMovie v9 Projects/Events to iMovie v10

I had a heck of a time finding info on transitioning from the previous version (v9.0.9) to the current version (v10.0.7). One of the problems I was having was getting the new version to recognize my old Projects and Events. After some digging here and elsewhere, I figured out what was wrong and how to fix it.

In my case, I had provisioned iMovie 9 to keep the Events folder on an external hard drive while the Projects folder was on my iMac's internal drive in the Movies folder. Don't ask me why they were separated; I can't remember why I did that or even if it was a mistake. Whatever the reason, it caused trouble when it came time to upgrade.

iMovie 10 keeps all the Projects and Events in a single Library file. By default, this Library is placed in your Movies folder on your Mac's internal hard drive. During the initial installation, iMovie will ask if you want to import the old versions Events and Projects. You can opt to do it right then or wait until later. When you do attempt to import these files, iMovie 10 will look in the Movies folder for the previous version's iMovie Events and iMovie Projects folders. If you have both of these folders in their default position, the new iMovie should be able to immediately import the files by copying them to the new version's Library. The old files will remain in their folders and will be useable by the previous version without any problems.

If you have the previous version's Projects and/or Events folders somewhere other than where iMovie 10 expects to find them, you may encounter an error when you try to import the old files. Even if the attempt fails, iMovie 10 creates extra files inside the old folder that prevent a successful import if you try it again. You'll need to look inside the old iMovie Events and iMovie Projects folders for a file called "UpdatedToiMovie10" and delete it from each folder. (In my case, I deleted these files from any drive that had these folders, not just the internal hard drive.) Restart iMovie 10 and select File > Update Projects and Events... to restart the import process. As long as the new iMovie Library is in the same folder as the old iMovie Projects and iMovie Events folders, this should proceed without a hitch.

If, like me, your old projects and events were stored at least partially on an external hard drive, you should consolidate them onto a single drive. DO NOT do this from the Mac's Finder. Move the projects and events to the drive where you want them by dragging them in iMovie 9's browser. Hold the Command key while dragging to move the files instead of just copying them. (If you copy the files instead of moving them, you'll have duplicates on both drives. It's not a problem, but the files will take up at least twice as much space on your drives.) Once the files are located where you want them, you can quit iMovie 9 and re-attempt the iMovie 10 import process by selecting File > Update Projects and Events...

I hope this helps anyone else having this issue. I also hope that anyone who can see where I've explained this incorrectly will please post a correction as a response.