The new advanced player allows you to set its layout for each slide individually. Indeed, this makes sense – if you don't have a video narration for one of your slides, why would you want to waste the screen estate on an empty video pane?
When you specify a layout for a slide, you can choose one of three values:
To specify a player layout for a given slide:
or
Double-click the layout icon of a given slide and choose a layout from the drop-down menu.