pipewire: Add new output plugin. Closes: #1048

[radioactiveman]

This is my attempt to port the PipeWire output plugin from Qmmp to Audacious.
Ilya Kotov, author of the related Qmmp code which is under GPL, allowed me to use the BSD license for our code base.

I'm using the plugin successfully for some time now, but further tests are of course appreciated. :)
Could you please support with the remaining things listed below? I don't know how to do them.

• Implement period_wait().
• Use the ring buffer from libaudcore instead of the raw char array.
• A few variables are still hard-coded, this should be cleaned-up.

Other questions:

• I assume the channel mappings in set_channel_map() can be reduced, since Audacious only supports up to 10 channels. Is this correct?
• Is it necessary to include all format mappings in to_pipewire_format()? The PulseAudio plugin for example only maps a few formats in to_pulse_format(). Why is that?
• Is the priority ok? Should it be lower than the PulseAudio plugin for now?

[mcarans]

Would be great to see this merged.

[PedroHLC]

LGTM, or better, sounding good to me (tested on NixOS).

[jlindgren90]

The biggest issue I see here is period_wait() isn't implemented. Calling pw_thread_loop_timed_wait() from write_audio() will potentially block the UI thread and make Audacious as a whole less responsive. Until we find a way to solve that, I would think it would be better to continue using the PulseAudio output plugin, as I believe that should be usable still with PipeWire?

[jlindgren90]

@radioactiveman It may enough to just move the pw_thread_loop_timed_wait() bit from write_audio() to period_wait(). Would you be able to make/test that change? (I am not using PipeWire on any of my own systems currently.)

[radioactiveman]

Thanks for the review @jlindgren90 and thanks @PedroHLC for testing. 👍
I will try to address the remarks in the next days when I have some time.

[radioactiveman]

@radioactiveman It may enough to just move the pw_thread_loop_timed_wait() bit from write_audio() to period_wait(). Would you be able to make/test that change?

Yes, this works. 👍 And I have noticed that the volume slider is in fact more responsive now, especially with the GTK interface.

[radioactiveman]

@jlindgren90: I have rebased this to master and addressed your review comments. CI is unfortunately not possible since the PipeWire package is too old on Ubuntu 20.04. Edit: Updated CI to use 22.04.

Could you please answer my two questions in the review? Thanks and looking forward to the merge. :)

[jlindgren90]

@radioactiveman Looks good to me. Thanks for all your work on this!

[birdie-github]

PipeWire uses/offers the exact same API as PulseAudio, in other words PA plugin is 100% compatible and sufficient for PipeWire.

There's no need to have two plugins. You may rename the old one from "PulseAudio plugin" to "PulseAudio/PipeWire plugin" and that's it.

[kaniini]

One plugin uses libpulse, and the other uses libpipewire directly. There's no need to support either sound system, but we do anyway.