def dvdnav(button)
      unless %w[up down left right menu select prev mouse].include? button.to_s
        raise ArgumentError, "Invalid button name"
      end
      command "dvdnav #{button}"
    end
def dvdnav(button)
      unless %w[up down left right menu select prev mouse].include? button.to_s
        raise ArgumentError, "Invalid button name"
      end
      command "dvdnav #{button}"
    end
presses the given dvd button
 available buttons are:
 :up :down :left :right :menu :select :prev :mouse