How to place some DisplayObject over OSMF VideoElement?

Question

I have successfully built an live stream application. It shows video from IP-camera via media server.
Now I need to handle user actions like click and area selection.
The problem is I can't draw area selection borders over VideoElement.displayObject. It is Video, so graphics lays lower than video.
I decided to make some MediaElement that has DisplayObjectTrait like this:
public class DisplayObjectElement extends MediaElement
     private var sprite: Sprite;
     public function DisplayObjectElement(sp:Sprite)
          super();
          sprite = sp;
     override protected function setupTraits():void{
          addTrait(MediaTraitType.DISPLAY_OBJECT, new DisplayObjectTrait(sprite));
          super.setupTraits();
and use DisplayObjectElement and VideoElement as children of ParallelElement:
container = new MediaContainer();addChild(container);
videoElement = new VideoElement(); //some graphics to test
selectionObject = new Sprite();
selectionObject.graphics.beginFill(0xff0000,1 );
selectionObject.graphics.drawCircle( 0, 0, 8 );
selectionObject.graphics.endFill();selectionElement = new DisplayObjectElement(selectionObject); var parElement:ParallelElement = new ParallelElement();
parElement.addChild(videoElement);
parElement.addChild(selectionElement); container.addMediaElement(parElement); mediaPlayer = new MediaPlayer();
mediaPlayer.media = parElement;
videoElement.resource = new URLResource("url to camera stream");
But selectionObject wasn't added to display list. Even when video is shown selectionObject.parent is null.
So I want to lay this selectionObject over VideoElement (with the same size and coordinates) and handle user actions and draw area selection borders on it.
I found simular solution here http://blog.six4rty.ch/2010/06/15/osmf-interactivespriteelement/ but it doesn't work for me.
I'm using OSMF 1.5.
How can I add my own control (Sprite or DisplayObject) over Video using OSMF framework?

Answer 1

I subclassed MediaElement without knowing of it's lifecycle:
MediaElement constructor calls setupTraits. And in DisplayObjectElement I call super() and then set up sprite = sp.
So when setupTraits() is called sprite == null.
Working DisplayObjectElement class looks like this:
public class DisplayObjectElement extends MediaElement
     public function DisplayObjectElement(sp:Sprite)
          super();
          addTrait( MediaTraitType.DISPLAY_OBJECT, new DisplayObjectTrait(sp) );