Update 2023-11-14 11:46:23

src/posts/2023-11-14_OpenBSD_sndio_and_multiple_devices.draft.pm

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+# OpenBSD sndio and mutiple devices
+
+## Automatic audio device switch
+
+OpenBSD automatically detects the system audio device. But often this is not enough. I want to plug in a USB headset and audio should automatically switch to it.
+
+You can start sndiod with additional `-F` flags, which define additional devices, which are switched to in order when they appear.
+
+```
+# sndiod -f rsnd/0 -F rsnd/1 -F rsnd/2 -F rsnd/3
+```
+
+You can set these flags permanently with:
+```
+# rcctl set sndiod flags -f rsnd/0 -F rsnd/1 -F rsnd/2 -F rsnd/3
+```
+
+This configuration allows up to 3 additional USB devices to be connected and sndiod will switch to the last one connected.
+
+If you have multiple devices connected and want to switch to a specific one, you can do so with:
+
+```
+$ sndioctl server.device=0
+$ sndioctl server.device=1
+$ sndioctl server.device=2
+...
+```
+
+## Record from one device, but play back on another...
+
+Let's say I want to connect USB microphone, but I want to to play back sound on another device.
+
+This works by setting the environment variables `AUDIORECDEVICE` and `AUDIOPLAYDEVICE` accordingly.
+
+Example:
+```
+export AUDIORECDEVICE=snd/1
+export AUDIORECDEVICE=snd/0
+```
+
+However, sndiod expects every device to play and record. So the above example would work to play on the system, but record on a headset.
+
+If the devices are more limited, the sndio flags need to be more specific, like this:
+
+```
+# rcctl set sndiod flags -f rsnd/0 -m play -s play -f rsnd/1 -m rec -s rec
+# rcctl restart sndiod
+$ export AUDIOPLAYDEVICE=snd/0.play
+$ export AUDIORECDEVICE=snd/1.rec
+```
+
+This creates a "play" sub device on the first audio device (system audio). And a sub device "rec" on the first USB device. The default is "play,rec", which would not work on my USB microphone. The -m switch describes what the device can do. The -s switch defines the sub device name.
+
+And now... everything works as expected.
+
+```
+$ aucat -o test.wav # record from microphone
+$ aucat -i test.wav # play on system speaker
+```