A filter for Wordpress oembed Block. Will set Youtube url to "youtube-nocookie.com" and will disable misc related videos (rel=). Enables Vimeo subtitles automatically using the browser language.

wordpress_oembed_utils.php

<?php 

function oembed_utils( $html ) {

	// set the default youtube url to youtube-nocookie.com
  $html = str_replace("www.youtube.com/embed","www.youtube-nocookie.com/embed", $html);
	
	// remove youtube random related videos
  $html = str_replace( "feature=oembed", "feature=oembed&rel=0", $html );

	// Set the Vimeo player subtitles accordingly to browser language
  if ($lang = substr($_SERVER['HTTP_ACCEPT_LANGUAGE'], 0, 2)) {
  	$pattern = '/(https\:\/\/player\.vimeo\.com\/video[^"]*)"/';
    $html = preg_replace($pattern, "$1&texttrack=" . strtolower( $lang ).'"', $html);
  }

  return $html;
}