First set allowsInlineMediaPlayback and mediaPlaybackRequiresUserAction to true.
Then check your iFrame HTML:
<html><body style='margin:0px;padding:0px;'><script type='text/javascript' src='http://www.youtube.com/iframe_api'></script><script type='text/javascript'>function onYouTubeIframeAPIReady(){ytplayer=new YT.Player('playerId',{events:{onReady:onPlayerReady}})}function onPlayerReady(a){a.target.playVideo();}</script><iframe id='playerId' type='text/html' width='640' height='480' src='http://www.youtube.com/embed/5_ofy9Ae87M?enablejsapi=1&rel=0&playsinline=1&autoplay=1' frameborder='0'></body></html>
Note playsinline=1 and autoplay=1 in HTML.
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