Parse media:content tag using Nokogiri

I need to extract the URL from this tag:

"media:content url="http://video.ted.com/talk/podcast/2011/None/MikeMatas_2011.mp4" fileSize="15533795" type="video/mp4" />"




doc = Nokogiri::XML(open("http://www.ted.com/talks/rss"))
doc.css('item').each do |item|
   puts item.at_xpath('media:content')['url']
end