Use .play()after adding it's src.
jQuery(document).ready(function($) {"use strict"; $("video").each(function() { var $source = $(this).find('source'); var src = $source.attr('data-src'); $source.removeAttr('data-src'); $source.attr('src', src); $source.detach().appendTo($(this)) $(this).get(0).play(); });});video { width: 420px; height: 230px;}<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script><video loop="loop" poster="http://placehold.it/420x230"><source type="video/mp4" data-src="http://techslides.com/demos/sample-videos/small.mp4"></video>