This AO has potential to be useful on platforms other than Linux. On
Windows in particular, PortAudio can make use of newer/better audio
APIs like WASAPI, instead of DirectSound.
As an implementation choice, the PortAudio callback API was used. The
blocking API might be a better match for mplayer's requirements, but
caused severe problems on Linux/ALSA (possibly PortAudio bugs).
wm4