The user is allowed a minimal amount of editing – one can type in a name, pick a different music, and remove certain images that they deem unfitting. Adding pictures is not permitted, though. File size is not a concern, as the mini-movies do not take much storage – for playback, the app streams the pictures and videos directly from your gallery. Only if you choose to export a certain vid will it create a larger file. After that, you are free to send it to your friends or import it in another editor.
Sounds like a nice and easy way to send pictures from your vacation... if you own an Xperia Z model, that is. If you want it - it can be downloaded from the Sony Update Center app.
Movie Creator screenshots
source: Xperia Blog via Android Community