/**
 *
 * Change default video slug to clip
 *
 * @param  array $args
 * @param  string $post_type
 * @return array
 */
function streamtube_child_change_video_post_type_slug( $args, $post_type ) {

    // change the video slug, for example: clip
    $new_slug = 'clip';

    if ( 'video' === $post_type ) {
        $args['rewrite']['slug'] = $new_slug;
    }

    return $args;
}
add_filter( 'register_post_type_args', 'streamtube_child_change_video_post_type_slug', 10, 2 );