PortAudio is a free, cross-platform, open-source, audio I/O library.  It
lets you write simple audio programs in C or C++ that will compile and run
on many platforms including Windows, Macintosh OS X, and Unix (OSS/ALSA).

It is intended to promote the exchange of audio software between developers
on different platforms.

PortAudio provides a very simple API for recording and/or playing sound
using a simple callback function or a blocking read/write interface.