How to Autoplay a YouTube video in Iframe embed

By Default a YouTube Iframe embed code don’t auto play a video  when embedded on a web page.

It can be auto played by simply adding this URL parameter in URL of video.

autoplay=1

So, The iframe code for a YouTube video which auto play when embedded on a page is

<iframe width="640" height="360" src="https://www.youtube.com/embed/LIn3tYCRZhk?rel=0&amp;autoplay=1" frameborder="0" allowfullscreen></iframe>