bytesTotal for Flash preloader AS3

Hello,

I am trying to build a Flash preloader. From this Flash file, I am dynamicly loading another Flash file. This is an SWF file of 30MB. I made it this big to test the progressbar.

While loading this SWF file, I want to show the progress of the loading in percentage. I have attached the used code.
I am showing the event.bytesTotal to the screen. But the strange thing is, that this bytesTotal is changing all the time, and it is always the same as bytesLoaded. How can I return the total file size so I can calculate the progress of the loading ?

var loader:Loader = new Loader();
loader.contentLoaderInfo.addEventListener(Event.COMPLETE, Dcomplete);
loader.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, showProgress);
loader.load(new URLRequest("movie.swf"));

function showProgress(event:ProgressEvent):void {
	var percentLoaded:Number = event.bytesLoaded/event.bytesTotal;
	percentLoaded = Math.round(percentLoaded * 100);
	textf.text = String(event.bytesTotal);
}

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