How to autoplay embed video using iframe

Changing from the old way of embedding videos to my blog to iframe, 

I found that I couldn't autoplay it with just adding autoplay=1, it doesn't work. 

I found this new coding here;

      https://productforums.google.com/forum/#!topic/youtube/99VJNpUKfIQ

deleting some of the options that I doesn't want, and are as below;

<iframe allowfullscreen="" frameborder="0" height="315" width="420" src="YOUR VIDEO SOURCE?VIDEO_ID&amp;version=4&amp;rel=0&amp;autoplay=1&amp;loop=1&amp;playlist=4v1Li36-0yY" ></iframe>

 it work well on pc, but still not autoplaying in smartphones though, but it's good enough for me now. ^^