lib/libsndio/sndio.7

.\" $OpenBSD: sndio.7,v 1.24 2020/07/18 05:01:14 ratchov Exp $
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.\" Copyright (c) 2007 Alexandre Ratchov <alex@caoua.org>
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.Dd $Mdocdate: July 18 2020 $
.Dt SNDIO 7
.Os
.Sh NAME
.Nm sndio
.Nd interface to audio and MIDI
.Sh DESCRIPTION
Programs access audio and MIDI hardware using the
.Nm sndio
library.
It allows both access through the
.Xr sndiod 8
server and raw access to the hardware.
The audio device or MIDI port, as well as the access method,
are designated by the sndio descriptor.
It is provided by the user with the program device selection method,
or with the
.Ev AUDIODEVICE
and
.Ev MIDIDEVICE
environment variables if there's no device selection method.
.Pp
Usually, programs access the hardware via the
.Xr sndiod 8
server, because raw access to the hardware is exclusive and
requires additional privileges.
The
.Xr sndiod 8
server supports multiple connections at a time, allowing multiple programs to
use the hardware concurrently.
It performs the necessary audio processing on the fly to
overcome any incompatibility between software and hardware.
Connections to
.Xr sndiod 8
may also be established through the network, including from virtual machines.
.Pp
The
.Xr sndiod 8
server exposes
.Em MIDI thru
ports, allowing one program to send MIDI data to other programs,
for instance to allow a sequencer to send events to a synthesizer.
.Pp
Additionally,
.Xr sndiod 8
exposes a MIDI port used to control audio programs using
standard MIDI Machine Control (MMC), MIDI Time Code (MTC),
and master volume messages.
.Sh AUDIO AND MIDI DESCRIPTORS
From the user's perspective every audio device or MIDI port
has a descriptor of the form:
.Bd -literal -offset center
type[@hostname][,servnum]/devnum[.option]
.Ed
.Pp
This information is used by programs to determine
how to access the audio device or MIDI port.
.Bl -tag -width "hostname"
.It Ar type
The type of the audio device or MIDI port.
Possible values are:
.Pp
.Bl -tag -width "midithru" -offset 3n -compact
.It Cm rsnd
Raw
.Xr audio 4
device.
.It Cm rmidi
Raw
.Xr midi 4
port.
.It Cm snd
Audio device exposed by
.Xr sndiod 8 .
.It Cm midithru
MIDI thru port created with
.Xr sndiod 8 .
.It Cm midi
MIDI port exposed by
.Xr sndiod 8 .
.It Cm default
Default audio device or MIDI port (see below).
.El
.It Ar hostname
The hostname or address where the remote
.Xr sndiod 8
server to connect to is running.
.It Ar servnum
The number of the
.Xr sndiod 8
server to connect to, corresponding to the integer specified using the
.Fl U
option of
.Xr sndiod 8 .
Useful only if multiple
.Xr sndiod 8
servers are running on the same system.
.It Ar devnum
Device number.
For hardware audio or MIDI ports, this corresponds to
the character device minor number.
For audio devices or MIDI ports created with
.Xr sndiod 8
it corresponds to the number of the corresponding
.Fl fq
option on the command line.
.It Ar option
Corresponds to the sub-device string registered using the
.Fl s
option of
.Xr sndiod 8 .
.El
.Pp
For example:
.Pp
.Bl -tag -width "snd/0.rear" -offset 3n -compact
.It Li rsnd/0
Raw access to first audio device.
.It Li rmidi/5
Raw access to MIDI port number 5.
.It Li snd/0
Audio device referred by first
.Fl f
option of
.Xr sndiod 8 .
.It Li snd/0.rear
Sub-device registered with
.Fl s Fa rear .
.It Li midithru/0
First MIDI thru port created with
.Xr sndiod 8 .
.El
.Sh DEFAULTS
If
.Cm default
is used as the audio device, the program will use the
one specified in the
.Ev AUDIODEVICE
environment variable.
If it is not set, the program first tries to connect to
.Li snd/0 .
If that fails, it then tries to use
.Li rsnd/0 .
.Pp
Similarly, if no MIDI descriptor is provided to a program
or when the reserved word
.Cm default
is passed as the device descriptor,
the program uses the one specified in the
.Ev MIDIDEVICE
environment variable.
If it is not set, the program first tries to connect to
.Li midithru/0 .
If that fails, it then tries to use
.Li rmidi/0 .
As long as
.Xr sndiod 8
is running, this allows programs to exchange MIDI data on
machines with no MIDI hardware by default, e.g. a MIDI player
could use a software synthesizer with no manual configuration
required.
.Sh AUTHENTICATION
For privacy reasons only one user may have connections to
.Xr sndiod 8
at a given time.
Users are identified by their
.Em session cookie ,
which is automatically generated by audio or MIDI programs
upon the first connection to the server.
The cookie is stored in
.Pa "$HOME/.sndio/cookie"
and contains 128 bits of raw random data.
.Pp
If a session needs to be shared between multiple users, they
can connect to the server using the same cookie.
.Sh ENVIRONMENT
.Bl -tag -width "AUDIODEVICEXXX" -compact
.It Ev AUDIODEVICE
Audio device descriptor to use
when no descriptor is explicitly specified to a program.
.It Ev MIDIDEVICE
MIDI port descriptor to use
when no descriptor is explicitly specified to a program.
.El
.Pp
These environment variables are ignored by
.Nm
if the program has the set-user-ID or set-group-ID bits set.
.Sh FILES
.Bl -tag -width "~/.sndio/cookie" -compact
.It Pa ~/.sndio/cookie
User's session authentication cookie.
.It Pa /dev/audioN
Audio devices.
.It Pa /dev/rmidiN
MIDI ports.
.El
.Sh SEE ALSO
.Xr aucat 1 ,
.Xr midicat 1 ,
.Xr sndioctl 1 ,
.Xr mio_open 3 ,
.Xr sio_open 3 ,
.Xr sioctl_open 3 ,
.Xr audio 4 ,
.Xr midi 4 ,
.Xr sndiod 8