def audio(hsh, key = nil)
      if !hsh.nil? && hsh.length
        if key.nil?
          hsh['mp3'] ? hsh['mp3'] : hsh['m4a'] ? hsh['m4a'] : hsh['ogg'] ? hsh['ogg'] : hsh['opus'] ? hsh['opus'] : hsh.values.first
        else
          hsh[key]
        end
      end
    end
def audio(hsh, key = nil)
      if !hsh.nil? && hsh.length
        if key.nil?
          hsh['mp3'] ? hsh['mp3'] : hsh['m4a'] ? hsh['m4a'] : hsh['ogg'] ? hsh['ogg'] : hsh['opus'] ? hsh['opus'] : hsh.values.first
        else
          hsh[key]
        end
      end
    end
Returns the audio file name of a given hash. Is no key as second parameter given, it
 trys first "mp3", than "m4a" and than it will return a more or less random
 value.

   {{ post.audio | audio:"m4a" }} => "my-episode.m4a"