Inserts content of a custom meta field using a shortcode. Use [mfs_custom_field field='my_field_name'] to insert any kind of meta field value inside of your posts.

shortcode-micro-plugin.php

<?php
/**
 * Plugin Name: Metafield Shortcode Micro Plugin.
 * Description: Inserts content of a custom meta field using a shortcode. Use [mfs_custom_field field='my_field_name'] to insert any kind of meta field value inside of your posts. Works both in WP v3.7 - 5.x and ClassicPress.
 * Version: 1.0
 * Author: Fabian Wolf
 * Author URI: https://usability-idealist.net/
 * License: GNU GPL v2
 */

/**
 * Usage instruction: 
 * 1. Save this file to your local system
 * 2. Upload the file to your wp-content/plugins/ folder
 * 3. Head over to the WordPress admin, and active the plugin under Plugins :)
 */

if( !function_exists( '_mfs_add_custom_field_shortcode' ) ) {
	function _mfs_add_custom_field_shortcode( $attr, $content = '' ) {
		$return = $content;
		
		// default attributes, which are being used if no value is set, but also, to only allow these specific variables
		
		$default_attr = array(
			'field'	=> '_my_custom_field_name',
			'title'	=> 'Videodauer:',
			'html_class'	=> 'custom_field_value_wrapper',
		);
		
		$params = shortcode_atts( $default_attr, $attr );
		
		/**
		 * Extract parsed parameters into the current scope. Avoid overriding existing variables.
		 * Also see @link https://www.php.net/extract
		 */
		extract( $params, EXTR_SKIP );
		
		$field_value = get_post_meta( get_the_ID(), $field, true );
		
		/** 
		 * NOTE: only generate return data if our field both exists AND contains any kind of data ;)
		 * Construct the return value in HTML.
		 */
		
		
		if( !empty( $field_value ) ) {
			$return = '<div';
			
			if( !empty( $html_class ) ) {
				$return .= ' class="' . $html_class . '"';
			}
			
			$return .= '">';
			
			if( !empty( $title ) ) {
				$return .= '<strong>' . $title . '</strong>';
			}
			
			// additional tag for better styling :)
			$return .= '<span>' .  $field_value . '</span>';
			
			$return .= '</div>';
			
		}
		
		return $return;
	}

	/**
	 * Usage:
	 * 
	 * [mfs_custom_field field="meta field name" title="optional title" html_class="my-html-class and-some moar"]
	 * 
	 * 
	 * @param string $field 		The name of the meta field to extract the content from. Required.
	 * @param string $title			Optional custom title.
	 * @param string $html_class	Optional HTML wrapper class.
	 */
	

	add_shortcode( 'mfs_custom_field', '_mfs_add_custom_field_shortcode' );
}

// closing tag intentionally left out ^^