<div id="mediaplayer"></div> 
<script>
$("#mediaplayer").kendoMediaPlayer({
    autoPlay: true,
    media: { title: "Kendo UI for jQuery: Welcome and Overview", source: "https://www.youtube.com/watch?v=UbkbVBNYZMc" }
});

setTimeout(function(){ 
    // get a reference to the media player widget
    var mediaPlayer = $("#mediaplayer").data("kendoMediaPlayer");
    // check if the media player is currently in fullscreen mode
    mediaPlayer.fullScreen();
    // force the widget to enter fullscreen
    mediaPlayer.fullScreen(true);
}, 1000)    

</script>