Pipewire audio support

[DemiMarie]

The problem you're addressing (if any)
Fedora 34 [will be switching to PipeWire], which brings security and functionality improvements. PipeWire is API and ABI compatible with PulseAudio, but I do not believe this compatibility extends to PipeWire plugins.

Fortunately, PipeWire has a multiprocess architecture, so we may be able to implement sinks and sources out of process. PipeWire also handles video input, meaning that we may be able to implement a paravirtualized camera system.

Describe the solution you'd like
PipeWire should be supported

Where is the value to a user, and who might that user be?
Fedora 34 users will have working audio.

Describe alternatives you've considered
We can force Fedora 34 to use PulseAudio, assuming it is still supported.

Additional context

Relevant documentation you've consulted

Related, non-duplicate issues

[0spinboson]

It looks like pipewire either doesn't like my usb microphone with headphone output, or there is an issue with the usb device forwarding in fedora-35, because when I connect my usb device, firefox / youtube refuses to playback any video because it seems to have problems outputting it to the audio device. (When I disconnect the usb device, video playback instantly resumes, after giving vague error messages. Playback via VLC works fine, although the volume scaling is terrible -- even volume set to 1/100 using alsamixer is pretty loud, 5/100 is almost unbearable, distortion starts quickly.)

Using journalctl -xe-t kernel, I also see a constant stream of "usb usb1: not yet implemented" multiple times each second, and "vhci_get_frame_number: 2570 callbacks suppressed" every 5 seconds. This is not an issue in a fedora-32-based qube, so I assume this is all related to the switch to pipewire.

(Running Qubes 4.1 up to date with current-testing, qubes-vm-kernel 5.10, 5.15.x in dom0.)

[DemiMarie]

Good news: PipeWire has a stable ABI for plugins!

[DemiMarie]

Bad news: the documentation is not sufficient for me to be able to create something that works. I will be filing some issues.