/**
  * setup plugin
  */
 public static function initialize()
 {
     if (!self::$initialized) {
         add_filter('meta_type_mapping', array(__CLASS__, 'meta_type_mapping'));
         add_action('admin_enqueue_scripts', array(__CLASS__, 'action_admin_enqueue_scripts'));
         add_action('admin_init', array(__CLASS__, 'check_voce_meta_api'));
         self::$initialized = true;
     }
 }
<?php

if (defined('ABSPATH')) {
    Voce_Post_Meta_Media::initialize();
}