What you want to do is set the fill opacity of the subpicture layer to zero, so that only the stroke is displayed for the layer.
Not sure I fully understand your menu button highlighting scheme – are you looking for a stroke around the video thumbnail and a circle (of a different color) also with a stroke? If so, you’ll need two subpicture layers, one for the outlines and the other for the solid (and use (=1) and (=2) prefixes for the different subpicture layers).