Conditional jquery element selection

I have a table:

<table id="codexpl">
<tr>
    <th>#</th>
    <th>Columna</th>
    <th>Relative</th>
    <th>Isso</th>
</tr>
<tr>
    <td>1</td>
    <td>This</td>
    <td>http://ift.tt/1ysHd2C;
    <td>Is</td>
</tr>
<tr>
    <td>2</td>
    <td>Coloumn</td>
    <td>two</td>
    <td>this</td>
</tr>
<tr>
    <td>3</td>
    <td>http://ift.tt/1ysHd2C;
    <td>not equals</td>
    <td>a</td>
</tr>
<tr>
    <td>4</td>
    <td>the</td>
    <td>Column</td>
    <td>real</td>
</tr>
<tr>
    <td>5</td>
    <td>first</td>
    <td>One</td>
    <td>Coloumn</td>
</tr>

I'd like to select only the tds that have urls in them and change their contents with

   $("td").each(function(){
          $('<div class="box"><iframe src="' + this.href + '" width = "500px" height = "500px"></iframe></div>').insertAfter(this);
         });

I've selected them before using jquery that looks like:

$('td').hover( function() {
          var contents = $( this ).html() ;
           if (contents.match("^http")) {

I'm wondering if you do something like this pseudocode:

 $('td' WHERE innerhtml=="^http"){....