Autoplay videos on scroll as window focuses

A video blog where the videos are 800x600 pixels (take most of browser screen). I am using html tag with attributes 'loop' and 'autoplay'

With more then 10 videos so far, the browser plays all of them a stalls!

I need a piece of code to play one video at a time as the user scrolls to the video in focus and pause the video as soon as out of scroll focus.