<script src="http://code.jquery.com/jquery-2.1.0.min.js"></script>

<script>

function postChange (psCopyFromId, psCopyToId)

{

   var copyFrom = document.getElementById(psCopyFromId);

   var copyTo = document.getElementById(psCopyToId);

​

​

   copyTo.value =copyFrom.value+'<iframe allowfullscreen style="overflow-x: hidden; overflow-y: hidden;" width="730" height="569" src="" frameborder="0">';

}

​

</script>

​

<input type="text" id="txt1" onKeyup="postChange(this.id, 'txt2');"></textArea>

<textArea id="txt2">

</textArea>