That hard to believe, as MP3 was standardized in 1989.

Didn't you mean AAC?

No, apparently he does mean MP3, but don't ask me how a patent filed in 1997 covers a standard that was finalized in 1991. (Was there a delay between date of invention and date of application, maybe involving provisional patents? I do not know the details of these things.)

http://www.tunequest.org/a-big-list-of-mp3-patents/20070226/

There is generally a delay between patents being filed and issues. I've heard of a number of very long waits before.

(I'm not an expert at all.)