//===================
// Timeline Preloader
// flashinit.com/blog
//===================

stop();

this.addEventListener(Event.ENTER_FRAME, handleLoading);

function handleLoading(event:Event):void{
	
	var total:Number = event.currentTarget.loaderInfo.bytesTotal;
	var loaded:Number = event.currentTarget.loaderInfo.bytesLoaded;

	trace(int((loaded/total)*100)+ "%");
	
	if (loaded >= total){
		// Done
		this.gotoAndStop(2);
		this.removeEventListener(Event.ENTER_FRAME, loading);
	}

}


//=================

Timeline preloader

ActionScript 3