No audio playback when default sink uses AUX channel map (PipeWire Pro Audio / HDMI)

[pqr3000]

Summary

No audio: PulseAudio rejects AUX channel map ([ None, None ]) on HDMI/Pro Audio sinks

Operating system

Linux

Steps to reproduce

1. Default sink channel map is aux0,aux1 (PipeWire Pro Audio / HDMI to monitor)
2. Open any page with audio/video
3. No sound

Expected behavior

Audio plays

Actual behavior

Silent; falls back to null output

URL for a reduced test case

N/A

HTML/SVG/etc. source for a reduced test case

N/A

Log output and (if possible) backtrace

Channel map is incompatible with PulseAudio: [ None, None ]
Failure in PulseAudio control thread: Channel map is incompatible with PulseAudio
Failed to create playback stream: Channel map is incompatible with PulseAudio; falling back to null output

Screenshots or screen recordings

No response

Build flags or config settings

No response

[Sm00shed]

Reproduced on 4d96e37. Reproducible without special hardware: simply force a positionless sink and make it the default:

pactl load-module module-null-sink sink_name=auxtest channels=2 channel_map=aux0,aux1
pactl set-default-sink auxtest

Then play any audio. Log:

Channel map is incompatible with PulseAudio: [ None, None ]
Failed to create playback stream: Channel map is incompatible with PulseAudio; falling back to null output

The channel map gets mangled by a round-trip conversion (Libraries/LibMedia/Audio/PulseAudioWrappers.cpp):

1. Sink map is aux0,aux1.
2. pulse_audio_channel_map_to_channel_map: no case for PA_CHANNEL_POSITION_AUX*, so both channels fall through to default and become Audio::Channel::Unknown. That is the [ None, None ] in the log.
3. create_stream converts it back via channel_map_to_pulse_audio_channel_map, where Audio::Channel::Unknown has no case and default turns it into PA_CHANNEL_POSITION_INVALID, so the map becomes [INVALID, INVALID].
4. pa_channel_map_valid() rejects any map containing INVALID, giving "Channel map is incompatible" and the null-output fallback.

So the rejected map is the one produced by the round-trip, not the sink's original map. Mono sinks hit the same path, since PA_CHANNEL_POSITION_MONO has no case either.