The "splash" screen can only be an image to be used as a placeholder until your app is able to start up. Even if you found a way to get a video to play, which I don't think is possible, it is against Apple's HIG for how the startup screen is supposed to be used.
It would be possible to load your video in its own view immediately after the splash screen. You would need to check for a first time run to determine whether to show it, unless you plan to show it each and every time. Hope this helps.
Apple Human Interface Guide