path: root/lib/libsndio/sndio.7

.\" $OpenBSD: sndio.7,v 1.27 2021/11/01 14:43:24 ratchov Exp $
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.\" Copyright (c) 2007 Alexandre Ratchov <alex@caoua.org>
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.Dd $Mdocdate: November 1 2021 $
.Dt SNDIO 7
.Os
.Sh NAME
.Nm sndio
.Nd audio and MIDI device descriptors
.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.
.Ss Server device descriptors
From the user's perspective, every audio device or MIDI port exposed by
.Xr sndiod 8
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 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 .
.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.
It corresponds to the number of the corresponding
.Fl f
or
.Fl q
option on the
.Xr sndiod 8
command line.
.It Ar option
Corresponds to the sub-device string registered using the
.Fl s
option of
.Xr sndiod 8 .
.El
.Ss Raw device descriptors
Every raw audio device or MIDI port has a descriptor of the form:
.Pp
.D1 Ar type Ns / Ns Ar devnum
.Pp
The
.Ar type
can be either
.Cm rsnd
or
.Cm rmidi .
The rsnd/0 device descriptor accesses the
.Pa /dev/audio0
device, rsnd/1 accesses
.Pa /dev/audio1 ,
and so on.
Similarly, rmidi/0 accesses
.Pa /dev/rmidi0
and so on.
.Ss Default Audio and MIDI devices
When no audio device descriptor is provided to a program
or when the reserved word
.Cm default
is used as the audio device, the program will use the
one specified in the
.Ev AUDIODEVICE , AUDIOPLAYDEVICE
and/or
.Ev AUDIORECDEVICE
environment variables.
If they are not set, the program first tries to connect to
.Li snd/default .
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.
.Ss 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 "AUDIOPLAYDEVICE" -compact
.It Ev AUDIODEVICE
Audio device descriptor to use
when no descriptor is explicitly specified to a program.
.It Ev AUDIOPLAYDEVICE
Audio device descriptor to use for play-only mode
when no descriptor is explicitly specified to a program.
Overrides
.Ev AUDIODEVICE .
.It Ev AUDIORECDEVICE
Audio device descriptor to use for record-only mode
when no descriptor is explicitly specified to a program.
Overrides
.Ev AUDIODEVICE .
.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
Raw audio devices.
.It Pa /dev/rmidiN
Raw MIDI ports.
.El
.Sh EXAMPLES
.Bl -tag -width "midithru/0" -compact
.It Li snd/0
Audio device referred to by the first
.Fl f
option of
.Xr sndiod 8 .
.It Li snd/rear
Sub-device registered with
.Dq -s rear .
.It Li midithru/0
First MIDI thru port created with
.Xr sndiod 8 .
.It Li default
Default audio or MIDI device.
.It Li rsnd/0
Direct hardware access to
.Pa /dev/audio0 .
.It Li rmidi/5
Direct hardware access to
.Pa /dev/rmidi5 .
.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