I would like to ask what the patent and or licensing restrictions of the MP3 file format are, and when did these arise?
The compression and decompression algorythms of MP3 are patented by the owner, Fraunhofer-Gesellschaft, and thus are not freely available for commercial products or commercial use of the technology. personal use of the MP3-software is allowed. Open-source-encoders and decoders are being allowed.
a patent-free alternative for MP3 is OGG Vorbis. other alternatives are free for non-commercial use, like SHN and FLAC, but in controdiction with MP3, those two don't loose quality, while MP3 does.
[EDIT] woops! I just realised I forgot to source this! source: https://en.wikipedia.org/wiki/MP3#Licensing.2C_ownership_and_legislation
The MPEG-LA group and Sisvel (Philips) prevent developers from adding MP3 support to their software packages without paying royalties.
MP3 has at least three separate companies that claim to have patents, Alcatel-Lucent, Thompson and AudioMPEG. All their claimed US MP3 patents are listed in the automatically generated MP3 patent list. The last of these patents expires in April of 2017. If you only look at the MP3 patents filed before December 1992 (one year after the decoding spec was published), then the last decoding patent expires in September of 2015. AudioMPEG claims that their patents cover MPEG-1 layers 1,2 and 3. The other companies just talk about Layer 3. So, at the minimum, fully decoding and encoding MPEG-1 audio is patented.
TL;DR: All MP3 patents could have expired in US after April 2017.