Credits go to IT168
My quick translation:
Galaxy S4 has a new feature called: SmartPause, which means when you are staring at the screen, the video playback will never pause and the screen will always be on. As long as you are not staring at the screen, the phone will detect you are not looking at the screen, and then video playback will pause itself.
OK, that's have a demo, for example, we open an album and find a video, and I am not looking at the screen just for now, and then, the video will pause automatically...