Create thumb from swf

I have a gallery that Im working on that shows thumbs of both image files and swf files from an xml file. I can create the thumbs fine with bitmapdata and draw. I load the files and when the onloadinit event fires I then create the bitmapdata and draw. This works fine for image files like jpegs and gifs but im having issues with the swf files. The onloadinit event is called after the actionscript executes in the swf. However the actionscript is rendering charts and that seems to happen after the onloadinit event. So the thumb is just of the stage in the swf file pre rendering of the animation. Is there anyway to know when the animation is stopped and then draw the bitmapdata?