Disable Related Videos For Your YouTube Videos

youtube-iframe.html

<iframe width="420" height="315" src="//www.youtube.com/embed/dQw4w9WgXcQ" frameborder="0" allowfullscreen></iframe>

youtube-no-related-videos.php

<?php
/*
Plugin Name: YouTube No Related Videos
Plugin URI: http://www.damiencarbery.com
Description: Set the 'rel=0' parameter on YouTube video urls.
Author: Damien Carbery
Version: 0.1
*/

add_filter( 'embed_handler_html', 'youtube_add_rel_param', 10, 3 );
function youtube_add_rel_param( $return, $url, $attr )
{
  // The generated html for the video will include 'rel=1' by default, unless 'rel=0' was specified in the url.
  // Simply change 'rel=1' to 'rel=0' if present.
  if (TRUE == strpos($return, 'rel=1')) {
    $return = str_replace('rel=1', 'rel=0', $return);
  }

  return $return;
}

youtube-url.txt

http://www.youtube.com/watch?v=dQw4w9WgXcQ