Ubuntu Manpage: sndio — interface to audio and MIDI

NAME

       sndio — interface to audio and MIDI

DESCRIPTION

The sndio audio and MIDI system provides access to audio and MIDI hardware and to services provided by
sndiod(8), summarized below.

Hardware audio(4) devices correspond to peripherals. Only one application may use any device at a given
time. Generally a limited number of encodings, sample rates and channel numbers are supported by the
hardware, which may not meet the requirements of audio programs.

To overcome hardware limitations and to allow multiple applications to share the hardware, sndiod(8) can
be used. It exposes one or more software sub-devices backed by the underlying hardware, while doing all
necessary conversions on the fly. It can mix multiple streams or split the hardware into multiple sub-
devices, to allow programs to use the hardware concurrently.

Hardware MIDI ports correspond to serial connectors provided by the midi(4) driver. They are typically
used to access MIDI hardware (synthesizers, keyboards, control surfaces, etc.), but they do not allow
applications to exchange information using the MIDI protocol.

Software MIDI thru boxes allow one application to send MIDI data to other applications connected to the
thru box (for instance a software sequencer can send events to multiple software synthesizers). There's
no hardware involved: thru boxes are created by sndiod(8).

Additionally, sndiod(8) exposes a MIDI port used to control and monitor audio streams in real time using
MIDI.

DEVICE NAMES

       From the user's perspective every audio interface, MIDI port, and sndiod(8) service has  a  name  of  the
       form:

                                 type[@hostname][,unit]/devnum[.option]

       This  information  is  used by audio and MIDI applications to determine how to access the audio device or
       MIDI port.

       type      The type of the audio device or MIDI port.  Possible values are:

                    rsnd      Raw audio(4) device.
                    rmidi     Raw midi(4) port.
                    snd       Audio device exposed by sndiod(8).
                    midithru  MIDI thru box created with sndiod(8).
                    midi      MIDI port exposed by sndiod(8).
                    default   Default audio device or MIDI port (see below).

       hostname  The hostname or address where the remote sndiod(8) server to connect to is running.

       unit      The number of the sndiod(8) server to connect to, corresponding to the integer specified  using
                 the  -U option of sndiod(8).  Useful only if multiple sndiod(8) servers are running on the same
                 system.

       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 sndiod(8) it corresponds to the
                 number of the corresponding -fq option on the command line.

       option    Corresponds to the sub-device string registered using the -s option of sndiod(8).

       For example:

          rsnd/0      First hardware audio device.
          rmidi/5     Hardware MIDI port number 5.
          snd/0       First audio device exposed by sndiod(8).
          snd/0.rear  Sub-device registered with -s rear.
          midithru/0  First MIDI thru box created with sndiod(8).

DEFAULTS

       If default is used as the audio device, the program  will  use  the  one  specified  in  the  AUDIODEVICE
       environment  variable.  If it is not set, the program first tries to connect to snd/0.  If that fails, it
       then tries to use rsnd/0.  This allows the sndiod(8) audio server to be used  by  default  and  the  bare
       hardware as fallback; programs don't have to be reconfigured when sndiod(8) is started or stopped.

       If default is used as the MIDI port, the program will use the one specified in the MIDIDEVICE environment
       variable.   If  it  is not set, the program first tries to connect to midithru/0.  If that fails, it then
       tries to use rmidi/0.  As long as 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.

AUTHENTICATION

       If a shared sndiod(8) server is running, for privacy reasons only one user may have connections to it  at
       a given time (though the same user could have multiple connections to it).  Users are identified by their
       session  cookie, which is automatically generated by audio or MIDI applications upon the first connection
       to the server.  The cookie is stored in $HOME/.sndio/cookie and contains 128 bits of raw random data.

       If a session needs to be shared between multiple users, they can connect to the  server  using  the  same
       cookie.

ENVIRONMENT

       AUDIODEVICE     Audio device that sio_open(3) uses if the application provides no device chooser.
       MIDIDEVICE      MIDI port that mio_open(3) uses if the application provides no MIDI port chooser.

       These  environment variables are ignored by sndio if the program has the set-user-ID or set-group-ID bits
       set.

FILES

       /dev/audioN     Audio devices.
       /dev/rmidiN     MIDI ports.