WP:Share WP media libraries across multisite network

network-shared-media.php

<?php
// Add filter that inserts our new tab
function nsm_menu($tabs) {
  $newtab = array('shared_media' => __('Network Shared Media', 'networksharedmedia'));
  return array_merge($tabs, $newtab);
}
add_filter('media_upload_tabs', 'nsm_menu');

// Load media_nsm_process() into the existing iframe
function nsm_menu_handle() {
  return wp_iframe('media_nsm_process');
}
add_action('media_upload_shared_media', 'nsm_menu_handle');

/*
 * media_nsm_process() contains the code for what you want to display. This function MUST start with the word 'media' in order
 * for the proper CSS to load.
 *
 * First, we switch to the blog containing all of the media. This is called up by the blog # found in the database.
 *
 * Then we call media_upload_library() which contains all of the code needed to show the library, select media sizes, and
 * insert into the post.
 */

function media_nsm_process() {
  switch_to_blog(3);
  media_upload_library();
}
?>

I realize this is 6 years old .. but I wanted to let anyone know that this doesn't work anymore for WP 4.0+ if they came across this GIST.