"main_w", "W", ///< width of the main video
"main_h", "H", ///< height of the main video
"overlay_w", "w", ///< width of the overlay video
"main_w", "W", ///< width of the main video
"main_h", "H", ///< height of the main video
"overlay_w", "w", ///< width of the overlay video