Parse ATOM in Ruby with custom namespaces

I'm trying to read this ATOM Feed (http://ffffound.com/feed), but I'm unable to get to any of the values which are defined as part of the namespace e.g. media:content and media:thumbnail.

Do I need to make the parser aware of the namespaces?

Here's what I 've got:

require 'rss/2.0'
require 'open-uri'

source = "http://ffffound.com/feed"
content = "" 
open(source) do |s| content = s.read end
rss = RSS::Parser.parse(content, false)