Append To SRC Attribute Parameters?

I have a string of text, with something similar to this in there:

Code:

<iframe src="http://www.youtube.com/emded/hIUHiu?test=somevalue">

and what I need to be able to do, is inject the parameter wmode=transparent as the FIRST parameter of the SRC attribute.

Hence, this:

Code:

<iframe src="http://www.youtube.com/embed/hiuHugiu?test=somevalue">

or indeed this:

Code:

<iframe src="http://www.youtube.com/embed/hiuHugiu">

Should become this:

Code:

<iframe src="http://www.youtube.com/embed/hiuHugiu?wmode=transparent&test=somevalue">

Here's my attempt. Is a regexp the way to go?

Code:

var test = '<iframe src="whatever.aspx?test=somevalue"></iframe>';
var pattern = '/src="(.*?)"/';
var replacement = 'src="${1}?wmode=transparent"';
test = test.replace(pattern,replacement);
alert(test)