I think the last MP3 patent will expire by the end of the year, I always thought AC-3 is younger than MP3 but well. (Almost the same age) MP3 is also an example

I think the last MP3 patent will expire by the end of the year, I always thought AC-3 is younger than MP3 but well. (Almost the same age) MP3 is also an example of prolonged patent validity, it was approved in 1991, published in 1993 but the last patent expires in 2017.