get subtitle from post content

add_filter( 'jnews_single_subtitle', 'custom_subtitile', 99, 3 );

function custom_subtitile( $subtitle, $post_id ) {
    if ( empty( $subtitle ) ) {
        $content  = get_post_field( 'post_content', $post_id );
        $content  = preg_replace( '/\[[^\]]+\]/', '', $content );
        $subtitle = wp_trim_words( $content, 25, '' );
    }

    return $subtitle;
}