Keyframes have been available in Final Cut Pro for many generations, however most people don't pay $300 for software. Luckily iMovie was given a stripped down version of this feature. The parts that are missing are specifically the ability to keyframe the main video, the ability to use cropping in a keyframe, and the ability to view the keyframe timeline. Luckily the feature is still present so this video will show you how to use it!
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Music For Intro:
http://incompetech.com/music/royalty-...