你应该钩住save_post 行动

add_action( \'save_post\', \'add_video_taxonomy\' );

function add_video_taxonomy( $post_id ) {

    // you should check if the current user can do this, probably against publish_posts
    // you should also have a nonce check here as well

    if( get_post_meta( $post_id, \'video_url\', true ) ) {
        wp_set_post_terms( $post_id, \'video\', \'your_custom_taxonomy_name\', true );
    }

}