Ok

ho trovato quest altro esempio che mi ha risolto il problema, lo posto magari potrebbe essere utile a qualcuno

var connection_nc:NetConnection = new NetConnection();
connection_nc.connect(null);
var stream_ns:NetStream = new NetStream(connection_nc);
my_video.attachVideo(stream_ns);
stream_ns.play("test8.flv");
//
stream_ns.onStatus = function(infoObject:Object) {
statusCode_txt.text = infoObject.code;
};

this.createTextField("time_txt", this.getNextHighestDepth(), 10, 10, 100, 22);
time_txt.text = "LOADING";

var time_interval:Number = setInterval(checkTime, 500, stream_ns);
function checkTime(my_ns:NetStream) {
var ns_seconds:Number = my_ns.time;
var minutes:Number = Math.floor(ns_seconds/60);
var seconds = Math.floor(ns_seconds%60);
if (seconds<10) {
seconds = "0"+seconds;
}
time_txt.text = minutes+":"+seconds;
}