proposal: PipeWire backend

proposals/2026-05-14_pipewire.md

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+# PipeWire support for Mixxx
+
+* **Owners:**
+  * `@pri-yan-shu`
+
+* **Implementation Status:** `Not implemented`
+
+> TL;DR: This proposes PipeWire audio API support to Mixxx, SoundDevice hotplug
+  for PipeWire, ability to route audio from Mixxx UI, and react to external changes.
+
+## Why
+
+PipeWire is an audio API for Linux. It replaces the multiple audio APIs already
+present on Linux, like ALSA, JACK, PulseAudio, and has compatibility layer for
+all those APIs. It also supports connecting any audio source/sink (from any
+application) to Mixxx, like the system audio inputs/outputs. This allows for
+flexibility in routing, for example adding an effect before input/after output.
+
+### Pitfalls of the current solution
+
+Currently Mixxx supports all audio APIs through PortAudio, which abstracts over
+audio APIs for multiple platforms. Features specific to a single API are not
+exposed, which leads to poor experience on Linux (for example,
+[incorrect naming of JACK ports](https://github.com/mixxxdj/mixxx/issues/5979)).
+
+* There is no hotplug for SoundDevices
+* As mentioned in the "Why" section, PortAudio only lets us route to and from
+  soundcards, and not the input/output of any arbitrary program
+
+## Goals
+
+Goals and use cases for the solution as proposed in [How](#how):
+
+* Refactor code related to current audio backends, and allow the selection of
+  PipeWire among the available backends.
+* Get feature parity with the current PortAudio backend. Ensure that drift and
+  jitter correction is happening properly in case of multiple DAC's
+* Provide accurate DAC sample playback timing info, which will be used for
+  jitter free waveform rendering.
+* Hotplug for audio devices on PipeWire
+* Support external patchbays by synchronizing routing UI with changes through external patchbays
+
+### Audience
+
+This change affects linux users using PipeWire.
+
+## Non-Goals
+
+* To be decided
+
+## How
+
+* The proposal will be implemented as a PipeWire client which listens for all
+  node/port/link objects (similar to existing PipeWire patchbays), and creates
+  SoundDevices accordingly. Since this happens for all source/sink available, not
+  just soundcard source/sink, we can route any source/sink to Mixxx. This will
+  work with the current routing UI in Sound Hardware preference page. Same
+  mechanism will be used to update the routing UI to reflect any changes made by
+  an external patchbay.
+
+* On Linux systems, PipeWire would show up in the Sound API option in the
+  preference panel, among other audio APIs offered by PortAudio. The existing
+  soundio code would be refactored into enumerators for different audio backends,
+  similar to Controller enumerators.
+
+## Action Plan
+
+The tasks to do in order to migrate to the new idea.
+
+* [ ] (week 1 25/5 to 31/5) Implement support for PipeWire backend.
+  * [ ] Refactor SoundManager into individual Enumerators (PortAudioEnumerator, PipewireEnumerator, NetworkEnumerator).
+  * [ ] Add PipewireEnumerator, SoundDevicePipewire, test working with program and soundcard input/outputs.
+* [ ] (week 2 01/6 to 07/6) Add soundcard hotplug support.
+* [ ] (week 3 08/6 to 14/6) Implement drift/jitter correction and sync with multiple soundcards
+* [ ] (week 4 15/6 to 21/6) Test drift/jitter correction and sync with multiple soundcards
+* [ ] (week 5 22/6 to 28/6) Modify PipeWire graph from Mixxx UI
+* [ ] (week 6 29/6 to 05/7) Update Mixxx UI from external graph changes
+* [ ] (week 7 06/7 to 12/7) Implement hardware soundcard volume access
+