My understanding is that software developers need a license to make MP3 decoders.
You may be interested in the wikipedia article about mp3:
Additionally, patent holders declined to enforce license fees on free and open source decoders, which allows many free MP3 decoders to develop.[59] Thus, while patent fees have been an issue for companies that attempt to use MP3, they have not meaningfully impacted personal use.
Essentially the mp3 IP holders realized about a decade ago that going after people who develop value for their IP made about as much sense as trying to tie your shoes with a shotgun blast.
I did see a discussion on this, but does anyone have a firm answer or know where one could find one.
Yes, a site like Hydrogenaudio where audio compression and audio technology is on topic.