Getting iPad to loop book trailer

Someone might have a solution for you (although not sure what a 'diaporama' is) - third post.

This is correct; if you make a folder in your photo library that has only the video file and then hit the 'slideshow' option ('diaporama?' wtf?) it will loop the file, as the file is the only thing in that particular folder. However, you have to make sure to sync the video into the photo library for that to work! (How to do that depends on what you're synching your photos from... iPhoto, the Pictures directory, etc.) If it's in the iPod/Video app, not the Photo collection, the slideshow trick won't work.

If that seems like too much effort, there's an iPad app called 'Video Loop' that will do this. Snag Video Loop off the App Store, sync it to the iPad, and then you'll see it in the 'Apps' tab under 'File Sharing.' Drag your MP4 file to Video Loop's file sharing pane, then you can play it on infinite loop within the app.