Re: "... some key MP3 patents have been allowed to expire ..."
MP3 isn't now "patent-free".
MP3 IP always had two parents: Thomson/Frauenhofer, and AT&T. Frauenhofer allowed its patents to lapse and mothballed the licensing program last month. Microsoft discovered the hard way a few years ago that Alcatel had a ton too. A few are still enforceable.