Been trying for ages but I finally solved the issue for the crossdomain.xml issue popping up and blocking my Youtube videos. The problem is NOT the crossdomain.xml file. The example feed that is given on the website is not VALID. If you add <title><description> and <link> to the channel element it starts to work.

So it should be like this

<rss version='2.0' xmlns:media='http://search.yahoo.com/mrss/' xmlns:atom='http://www.w3.org/2005/Atom'>


<channel>


<title>Website</title>


<description>Website Title</description>


<link>http://www.website.com</link>


<item>


<title>Image or Video</title>


<link>Image or video Link</link>


<media:description></media:description>


<media:thumbnail url='url' />


<media:content type='image/jpeg' url='url' />


</item>


</channel>


</rss>

Wonder if I can sue for lost time… Oh well.