I'm not sure you can do what you are describing via the
FLVPlayback component fullscreen button. If you want your 1600x1200
stage with menu to be in fullscreen you would need to create a
button which invokes the stage's fullScreen displayState like:
function onClick(event:MouseEvent):void {
stage.displayState="fullScreen";
}
Maybe you are already doing that, but once you set the stage
to fullscreen, the FLVPlayback component button's going to conflict
and toogle in and out of fullscreen. I think you will need to make
your own custom "fullscreen" button for the player which gets the
stage size and scales the FLVPlayback instance to that dimension.