I realize this is an old question but this answer might help someone down the road:
Android (and iOS both) disabled the autoplay
tag in HTML5 video
nodes in the Chrome or native browser. Playing a video requires user interaction (onClick or onMouseOver or something). However, one can autoplay videos in one's own WebView if necessary.
To autoplay videos in an Android Webview, post Android 4.4:
webview.setWebChromeClient(new WebChromeClient());
webview.getSettings().setMediaPlaybackRequiresUserGesture(false);