This is possible on the iPhone; the capability can be found in the AVFoundation framework. The classes of interest to you are AVMutableVideoComposition and AVVideoCompositionCoreAnimationTool. Using the AVMutableVideoComposition's animationTool
property, you can use a AVVideoCompositionCoreAnimationTool to add a Core Animation layer on top of your video.
These video editing capabilities were added in iOS 4.0, and highlighted at WWDC 2010 in the session titled Editing Media with AV Foundation. If you are a registered Apple developer, you can view this session video by following the link at http://developer.apple.com/videos/wwdc/2010/. When browsing the session videos in iTunes, look for session 407 under Graphics and Media.
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