Because you are using a 3rd party mp3 decoder, you only need to pay the 'mp3 patent-only license' It is broken down as either a one-time $50,000 payment, which none of us can afford, or you can pay $0.75 for each program sold. If you are also using a 3rd party MP3 encoder in your program, you will have to pay an additional $2.50 per unit sold. They also have a $15,000 minimum annual royalty fee.
There are different royalties for electronic distribution, broadcasting and streaming mp3 files. So if your program also has the ability to send mp3 audio streams to other programs... Well that's another 2% + $2,000 yearly minimum.
As a shareware developer, you may be able to get away from paying the yearly minimums.
Overall this entire MP3 licensing is total BS as neither Thomson MM nor Fraunhofer IIS-A, developed the MP3 compression algorithm. Fraunhofer contributed
technology to the development of the MPEG-1 and MPEG-2 audio standards, as did other developers/companies. Fraunhofer simply adapted existing MPEG compression methods and applied them to Audio files. They DO NOT own MP3, but they do own patents on technologies that are part
of MPEG standards. MPEG standards are owned by the International Standardisation Organisation (ISO) http://www.iso.ch
Take a look @ http://web.media.mit.edu/~eds/mpeg-patents-faq
for some details.
I wonder if I can patent this Internet thing and retire!
Hope it helps.