Sink device handling in wasapi backend

[maxbachmann]

We need a playback device + context that is always valid and "playing" even when there is no usable output device. Both at startup and during hot-plug at runtime. So when there is no device connected we want the behaviour of the null backend and otherwise the behaviour of the wasapi backend.

Our current local patch is maxbachmann@364c2d9. With this we can start with/without devices and call alcReopenDeviceSOFT whenever there is a device change/removal.

Is there already way to achieve this without our patch?

[kcat]

You could probably define a virtual device for the system that takes and processes playback streams and just doesn't play them on any real device. You wouldn't need to modify OpenAL Soft then, though it would be specific to your system. There isn't a way to do this within OpenAL Soft itself currently.

Ideally any changes to enable this behavior shouldn't be within specific backends, and it shouldn't automatically happen when the requested device doesn't exist. A better option would be to allow the NullBackend to be used concurrently with the normal backend, but I'd be wary of that always enumerating/reporting a usable output device (or using it by default) when there are no real devices currently available on the system.

[maxbachmann]

A virtual device isn't really a solution for us since this isn't running on our own systems.

The change in the backend was made because that's the simplest patch for us to create and maintain when upgrading openal given that we only really have to worry about wasapi (pulseaudio/pipewire usually have a default sink device). I didn't expect this specific patch to be upstreamable since as you said it isn't a generic solution and is always enabled. With the patch our game is able to always behave as if there is an audio device and users just being able to hotplug their audio device during runtime.