How to put video from iTunes to Kindle Fire?

As we know, iTunes videos are only available in one iTunes users account on the limited playing devices or media players. So what should I do if I want to put music/video from iTunes to Kindle Fire? It is not convenient for us to transfer iTunes videos to other video playing devices. But there are also many people want to do this. All of them wonder "If there is any way to let the purchased videos on itunes to play on Kindle Fire?"