Use CSS for responsive sizing
This option uses CSS to resize the video player. It does not rely on the orientation change event and is very fast and fluid. Since the video player size is driven by CSS and the aspect ratio of 16:9 is maintained, the height of the player may exceed the visible container height on certain mobile devices. The container may be scrolled should this occur.
If you check this option, and if the Video Player is contained in a 'Container' control, be sure to set these properties on the containing 'Container':'Alignment' = 'Left', 'Prevent container float' = checked.