[fljot]

По-моему, у флекса такая иделогия

private var _source:String;
private var sourceChanged:Boolean = false;
public function set source(value:String):void
{
    if (_source == value) return;
    _source = value;
    sourceChanged = true;
    invalidateProperties();
}
override protected function createChildren():void
{
    //TODO Auto-generated method stub
    super.createChildren();
 
    if (!player)
    {
	player = new VideoDisplay();
	player.addEventListener(VideoEvent.READY, player_readyHandler);
	player.addEventListener(VideoEvent.COMPLETE, player_completeHandler);
	this.addElement(player);
    }
}
 
override protected function commitProperties():void
{
    super.commitProperties();
    if (sourceChanged && player)
    {
        player.source = source;
        sourceChanged = false;
    }
}