iMovie '11: Choosing the correct export option for your iPhone or iPod touch
Movie ’11 can share video files in a variety of ways, including an option to share to iTunes for playback on an iPhone, iPod, Apple TV, or computer. However, you cannot sync an HD 720p video to an iPhone earlier than iPhone 4, or to an iPod touch earlier than iPod touch (4th generation). If you attempt to, you will receive an alert message stating that the video cannot be played (see Figure 1).
If you want to view your iMovie project on earlier model iPhone or iPod touch, use the Mobile or Medium size export options in iMovie. When sharing to iTunes and other destinations, iMovie ’11 displays a window (shown below) that indicates recommended video sizes for use on various products. The HD 720p setting indicates it is recommended for iPhone, but this is only true for iPhone 4 and iPod touch (4th generation) or later.
For more information about supported video formats, please see the Technical Specifications page.