gistfile1.aw

<?php
  /**
   * Display a thumbnail from YouTube based off the embed code saved in the
   * video post format metabox used by the CF Post Formats plugin
   *
   * @link https://github.com/crowdfavorite/wp-post-formats
   * @link http://stackoverflow.com/a/6382259
   */

  global $post;

  $video_details = get_post_meta($post->ID, '_format_video_embed', true);
  
  if (preg_match('%(?:youtube(?:-nocookie)?\.com/(?:[^/]+/.+/|(?:v|e(?:mbed)?)/|.*[?&]v=)|youtu\.be/)([^"&?/ ]{11})%i', $video_details, $match)) {
    $video_id = $match[1];
  }

  if (isset($video_id)) { ?>
    <a href="<?php the_permalink(); ?>"><img src="http://img.youtube.com/vi/<?php echo $video_id; ?>/0.jpg"></a>
  <?php } 
?>