The following paragraph from sndio(7) probably no longer applies as is: 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 raw hardware as fallback; programs don't have to be reconfigured when sndiod(8) is started or stopped.
With the recent audio(4)/midi(4) change (as described at http://www.openbsd.org/faq/upgrade67.html) users cannot access the raw devices any more, so e.g. $ aucat -o /tmp/file.wav ^C $ doas rcctl stop sndiod sndiod(ok) $ aucat -o /tmp/file.wav default: couldn't open audio device instead of falling back to rsnd/0. (I'll leave the rewording to Alexandre.) Jan