if( ! function_exists( 'videotube_post_archive_to_video_archive' ) ){
    /**
     * @param unknown_type $args
     * @return string
     */
    function videotube_post_archive_to_video_archive( $args ) {
        $args['post_type'] = 'video';
        return $args;
    }
    add_filter( 'widget_archives_args' , 'videotube_post_archive_to_video_archive', 10, 1 );
    add_filter( 'widget_archives_dropdown_args' , 'videotube_post_archive_to_video_archive', 10, 1 );
}