Controllers are all the means that in the end display images on a screen. You could think of a (mini) computer or an external media player, to display videos or photos in a loop. The beauty of a media player is that as soon as the power on location is switched on it begins to play. Making it a hassle-free experience for you. Or imagine cameras displaying real-time images on screen. Or complete virtual reality sets putting you in a complete other world thanks to the virtual reality goggles.