How about BASS audio library
"BASS is an audio library for use in software on several platforms. Its purpose is to provide developers with powerful and efficient sample, stream (MP3, MP2, MP1, OGG, WAV, AIFF, custom generated, and more via OS codecs and add-ons), MOD music (XM, IT, S3M, MOD, MTM, UMX), MO3 music (MP3/OGG compressed MODs), and recording functions. All in a compact DLL that won't bloat your distribution."
: "BASS is free for non-commercial use. If you are a non-commercial entity (eg. an individual) and you are not making any money from your product (through sales, advertising, etc), then you can use BASS in it for free."
For completeness i would add "LAME
]- a high quality MPEG Audio Layer III (MP3) encoder licensed under the LGPL."