Server device descriptors¶

From the user's perspective, every audio device or MIDI port exposed by sndiod(8) has a descriptor of the form:

type[@hostname][,servnum]/[devnum|option]

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

type

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

snd

Audio device exposed by sndiod(8).

midithru

MIDI thru port created with sndiod(8).

midi

MIDI port exposed by sndiod(8).

hostname

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

servnum

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. It corresponds to the number of the corresponding -f or -q option on the sndiod(8) command line.

option

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

Raw device descriptors¶

Every raw audio device or MIDI port has a descriptor of the form:

The type can be either rsnd or rmidi. The rsnd/0 device descriptor accesses the /dev/audio0 device, rsnd/1 accesses /dev/audio1, and so on. Similarly, rmidi/0 accesses /dev/rmidi0 and so on.

Default Audio and MIDI devices¶

When no audio device descriptor is provided to a program or when the reserved word default is used as the audio device, the program will use the one specified in the AUDIODEVICE, AUDIOPLAYDEVICE and/or AUDIORECDEVICE environment variables. If they are not set, the program first tries to connect to snd/default. If that fails, it then tries to use rsnd/0.

Similarly, if no MIDI descriptor is provided to a program or when the reserved word default is passed as the device descriptor, the program uses 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¶

For privacy reasons only one user may have connections to sndiod(8) at a given time. Users are identified by their session cookie, which is automatically generated by audio or MIDI programs 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.