NAME

ossaudio — Open Sound System emulation

LIBRARY

OSS Audio Emulation Library (libossaudio, -lossaudio)

SYNOPSIS

#include <soundcard.h>

DESCRIPTION

The ossaudio library provides an emulation of the Open Sound System audio interface.

Use the native audio(4) and mixer(4) interfaces for new programs, and this emulation library only for building code written for other operating systems.

Mixer Control Map

The following table summarizes the mappings from native interface device names to OSSv3 mixer controls.

Native Device Name	OSS Mixer Control
*.mic	SOUND_MIXER_MIC
*.line	SOUND_MIXER_LINE
*.cd	SOUND_MIXER_CD
*.dac	SOUND_MIXER_PCM
*.aux	SOUND_MIXER_LINE1
*.record	SOUND_MIXER_IMIX
*.master	SOUND_MIXER_VOLUME
*.treble	SOUND_MIXER_TREBLE
*.bass	SOUND_MIXER_BASS
*.speaker	SOUND_MIXER_SPEAKER
*.output	SOUND_MIXER_OGAIN
*.input	SOUND_MIXER_IGAIN
*.fmsynth	SOUND_MIXER_SYNTH
*.midi	SOUND_MIXER_SYNTH

COMPATIBILITY

The ossaudio interface aims to be compatible with the Open Sound System version 4, as described in:

4Front Technologies, OSS 4.x Programmer's Guide, http://manuals.opensound.com/developer/, 2007.

HISTORY

The ossaudio library first appeared in NetBSD 1.3.

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 FreeBSD and Solaris, and a large body of code exists supporting it.

BUGS

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.
NetBSD AUDIO_MIXER_SET control types cannot be accurately represented in the OSSv4 mixer API, so are treated as enums.
Per-stream volume (i.e. 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.
Linux, FreeBSD, and Solaris provide /dev/dsp and /dev/mixer devices in place of the /dev/audio and /dev/mixer devices this compatibility layer must be accessed through on NetBSD. However, changing this is typically trivial when porting programs.
The emulation only covers ioctl(), there are other differences as well. E.g., on a write that would block in non-blocking mode Linux returns EINTR whereas NetBSD 1.3 returns EAGAIN.
The emulation uses a #define for ioctl() so some obscure programs can fail to compile.