libao is a cross-platform audio library that allows programs to
output audio using a simple API on a wide variety of platforms.
On FreeBSD, it currently supports:
* null output
* raw output
* AU files
* WAV files
* OSS (Open Sound System)
* ESD (ESounD or Enlightened Sound Daemon)
* aRts (KDE sound server)
WWW: http://www.xiph.org/ao/