MP3 is now substantially patent free due to patents expiring
"The basic MP3 decoding and encoding technology is patent-free in the European Union, all patents having expired there by 2012 at the latest. In the United States, the technology became substantially patent-free on 16 April 2017 " https://en.wikipedia.org/wiki/MP3
Free alternatives are Ogg and Flac https://xiph.org/flac/faq.html
