ActionScript 3.0 :: RegExp - Look For ID In Input Text String

ActionScript Code:
input.text = "[URL]";
function PlayVideo(event:MouseEvent):void {
switch (event.type) {
case "click":
var findVideo:RegExp = /(?<=?v=)([a-zA-Z0-9_-])+/;
trace(findVideo.exec(input.text));
break;
}}

I don't know what video this is (just picked it randomly off of the front page), but by clicking a button, the RegExp is called, looks for an ID in the input.text String, but when it does and I trace it, it gives me this:

ActionScript Code:
QGsGJlCpor4,4
What's with the ,4? How do I get rid of that?