Cropped Video in iMovie – How to Overlay a Cropped Video on Another Video in iMovie

iMovie only supports the H.264 format, and will only load videos from two places:

• Camera Roll
• Synced iPhoto Library via iTunes (Photos Tab → Sync Photos from iPhoto → Include Videos)

As you've noticed, videos in your iTunes → Movies folder will only sync to the Videos app, and will not appear in iMovie.

The process is not at all convenient, but here's a video detailing how to convert a video to the right format on a Mac, and then get it into iMovie on an iPad: https://www.youtube.com/watch?v=oF8-sDmD_1Y. He uses an app called StreamClip Video Converter to convert to H.264. You might be able to get away with exporting that format from iMovie on your Mac instead. iMovie is picky about the format though. If you have trouble, try to reproduce the settings in the video exactly.

For apps that don't support two-factor authentication, such as iMovie, you need to generate an application-specific password. This is a computer generated password that can be used to give an app access to Google services, but is intended for use in a single app.

Go here to manage your connected apps and application-specific passwords. Once you generate one (be sure to label it as "iMovie password" or similar), copy it into iMovie making sure to use your full Gmail address as the "Account Name", then you're done with it.

There's intentionally no way to view the password again, the only possible action is to revoke it. This way your account still stays secure as long as the app stores the password securely (and if it doesn't, you can always revoke that one password without causing problems for the rest of the account).