Getting started with creating your own custom shortcodes in WordPress

Read out Custom Field Value via Shortcode in WordPress

function output_my_custom_field($atts, $content = null) {
	$a = shortcode_atts([
		"field"	=> "_my_custom_field_name",
		"title"	=> "Videodauer:",
		"class"	=> "custom_field_value_wrapper",
	], $atts);
	$return_string = '';
	if(get_post_meta(get_the_ID(), $a["field"], true) != '') {
		$my_custom_field_value = get_post_meta(get_the_ID(), $a["field"], true);
		$return_string = '<div class="' . $a["class"] . '"><strong>' . $a["title"] . '</strong> ' . $my_custom_field_value . '</div>';
	}
	return $return_string;
}
add_shortcode('my_custom_field_value', 'output_my_custom_field');

/* Anwendung:
[my_custom_field_value field="_my_custom_field_name"]
*/