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.Dd October 20, 2020
.Dt OSSAUDIO 3
.Os
.Sh NAME
.Nm ossaudio
.Nd Open Sound System emulation
.Sh LIBRARY
.Lb libossaudio
.Sh SYNOPSIS
.In soundcard.h
.Sh DESCRIPTION
The
.Nm
library provides an emulation of the Open Sound System audio interface.
.Pp
Use the native
.Xr audio 4
and
.Xr mixer 4
interfaces for new programs, and this emulation library only for
building code written for other operating systems.
.Ss Mixer Control Map
The following table summarizes the mappings from native interface
device names to OSSv3 mixer controls.
.Bl -column ".Sy Native Device Name" "SOUND_MIXER_SPEAKER"
.It Sy "Native Device Name" Ta Sy "OSS Mixer Control"
.It *.mic Ta SOUND_MIXER_MIC
.It *.line Ta SOUND_MIXER_LINE
.It *.cd Ta SOUND_MIXER_CD
.It *.dac Ta SOUND_MIXER_PCM
.It *.aux Ta SOUND_MIXER_LINE1
.It *.record Ta SOUND_MIXER_IMIX
.It *.master Ta SOUND_MIXER_VOLUME
.It *.treble Ta SOUND_MIXER_TREBLE
.It *.bass Ta SOUND_MIXER_BASS
.It *.speaker Ta SOUND_MIXER_SPEAKER
.It *.output Ta SOUND_MIXER_OGAIN
.It *.input Ta SOUND_MIXER_IGAIN
.It *.fmsynth Ta SOUND_MIXER_SYNTH
.It *.midi Ta SOUND_MIXER_SYNTH
.El
.Sh COMPATIBILITY
The
.Nm
interface aims to be compatible with the Open Sound System version 4, as
described in:
.Pp
.Rs
.%A 4Front Technologies
.%T OSS 4.x Programmer's Guide
.%U http://manuals.opensound.com/developer/
.%D 2007
.Re
.Sh SEE ALSO
.Xr ioctl 2 ,
.Xr audio 4 ,
.Xr midi 4 ,
.Xr mixer 4
.Sh HISTORY
The
.Nm
library first appeared in
.Nx 1.3 .
.Pp
The Open Sound System up to version 3 was originally the preferred
API for writing audio code under Linux until ALSA became the new default
in Linux 2.6.
It remains the preferred API in
.Fx
and Solaris, and a large body of code exists supporting it.
.Sh BUGS
.Bl -bullet
.It
The emulation is incomplete.
Some less popular features are not emulated (e.g. sync groups), but the
essential ioctls used by the majority of software are covered.
.It
.Nx
.Dv AUDIO_MIXER_SET
control types cannot be accurately represented in the OSSv4 mixer API,
so are treated as enums.
.It
Per-stream volume (i.e.
.Dv SNDCTL_DSP_SETPLAYVOL )
is not currently implemented as in OSSv4, and will instead modify the
global volume.
Applications need to provide samples with the appropriate gain.
.It
Linux,
.Fx ,
and Solaris provide
.Pa /dev/dsp
and
.Pa /dev/mixer
devices in place of the
.Pa /dev/audio
and
.Pa /dev/mixer
devices this compatibility layer must be accessed through on
.Nx .
However, changing this is typically trivial when porting programs.
.It
The emulation only covers
.Fn ioctl ,
there are other differences as well.
E.g., on a write
that would block in non-blocking mode Linux returns
.Er EINTR
whereas
.Nx 1.3
returns
.Er EAGAIN .
.It
The emulation uses a #define for
.Fn ioctl
so some obscure programs
can fail to compile.
.El