CKEditor

HTML

<script src="http://ckeditor.com/apps/ckeditor/4.0/ckeditor.js"></script>
<link rel="stylesheet" href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/css/bootstrap-combined.min.css">
<script src="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/js/bootstrap.min.js"></script>
<h3>CKEditor 4:</h3>

<textarea id="editor1">Test</textarea>

JavaScript

CKEDITOR.replace('editor1');
video_id = "lLi1Lx2xTKI";

$.getJSON('http://gdata.youtube.com/feeds/api/videos/'+video_id+'?v=2&alt=jsonc',function(data,status,xhr){   
    CKEDITOR.instances.editor1.setData(data.data.description); 
});