/**
 *
 *
 * Filter the thumbnail size.
 *
 * @since 1.0.0
 *
 */
function videotube_child_filter_video_thumbnail_size( $size ){
    return 'full';
}
add_filter( 'video_thumbnail_size', 'videotube_child_filter_video_thumbnail_size', 10, 1 );