Provided by: sndiod_1.1.0-3_amd64 bug

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/.aucat_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 to use if the application provides no device chooser.
     MIDIDEVICE      MIDI port to use if the application provides no MIDI port chooser.

     Environment variables are ignored by programs with the set-user-ID or set-group-ID bits set.

FILES

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

SEE ALSO

     mio_open(3), sio_open(3), audio(4), midi(4), sndiod(8)