Auto addEventListener("stateChange", listenerObject)

Code that I found.

[]I need to modify this code but have no idea where to start. First I need this code to update every half second. As it is currently written it only updates when I press a button. I am using it as a running time code for my movie.
]I also need to be able to display the output to my flash app, it currently only outputs to my output box when testing.[/LIST]

var listenerObject:Object = new Object();
listenerObject.stateChange = function(eventObject:Object):Void {
trace(my_video.state + ": playhead time is: " + my_video.playheadTime);
my_video.addEventListener("stateChange", listenerObject);