No sound inside Ubuntu Core 24.04 on RPi 5

gmattinson · January 21, 2025, 4:34pm

I can’t get pulseaudio working on a Raspberry Pi 5 using Ubuntu Core 24.04.

My gadget snap started from: GitHub - canonical/pi-gadget at 24 With the following changes:

Makefile line 150: kms instead of fkms
config.txt-common line 17: uncomment hdmi_drive=2

My image started from: models/ubuntu-core-24-pi-arm64.json at master · canonical/models · GitHub With the following changes:

Custom authority-id & brand-id due to the custom gadget
Grade dangerous

If I run aplay -l as root, it lists vc4hdmi0 and vc4hdmi1, so ALSA is able to see the HDMI monitor. And I’m able to hear a .wav file played with aplay.

I have installed Pulse Audio from the beta channel: sudo snap install --beta pulseaudio

But, pulseaudio.pactl list sinks only lists Dummy Output. How can I get Pulse Audio to detect the HDMI sinks which ALSA is using?

ogra · January 22, 2025, 7:51am

You could try building my pulse snap from:

It has some extra alsa integration the snap in the store does not have…

gmattinson · January 22, 2025, 2:53pm

@ogra,

Thanks for the reply - your knowledge on this forum is amazing.

I downloaded & built your pulse-server, and snapped it onto the Pi 5, but unfortunately when run as root, pulse-server.pactl list sinks still only outputs the Dummy Output.

I first tried it without pulseaudio installed, and it said “pa_context_connect() failed: Connection refused” which leads me to believe that pulse-server relies on pulseaudio?

ogra · January 23, 2025, 10:07am

pulse-server ships pulseaudio (this is in fact its only purpose )

I wonder if the Pi5 simply handles HDMI audio different than its former versions (i sadly don’t have a Pi5 around to try) or if there are still kernel patches missing (remember how new the hardware is, the pi Ubuntu kernel predates its release)

gmattinson · January 23, 2025, 2:10pm

@ogra, I had assumed pulse-server was a replacement for pulseaudio, which is why I tried without pulseaudio installed first.

Doesn’t pulseaudio / pulse-server depend on ALSA? aplay works, so to me it seems like a problem connecting pulseaudio / pulse-server to ALSA, not a problem from ALSA to the HDMI port. Are any environment variables, snap connections, or libraries required to make pulseaudio / pulse-server work?

user@localhost:~$ snap connections
Interface              Plug                                Slot                           Notes
alsa                   pulse-server:alsa                   :alsa                          manual
alsa                   pulseaudio:alsa                     :alsa                          -
audio-playback         pulse-server:playback               pulse-server:audio-playback    -
audio-playback         pulseaudio:playback                 pulse-server:audio-playback    -
custom-device          console-conf:terminal-control       console-conf:terminal-devices  -
hardware-observe       console-conf:hardware-observe       :hardware-observe              -
hardware-observe       pulseaudio:hardware-observe         :hardware-observe              -
network                console-conf:network                :network                       -
network                pulse-server:network                :network                       -
network                pulseaudio:network                  :network                       -
network-bind           pulse-server:network-bind           :network-bind                  -
network-bind           pulseaudio:network-bind             :network-bind                  -
network-control        console-conf:network-control        :network-control               -
network-observe        console-conf:network-observe        :network-observe               -
network-setup-control  console-conf:network-setup-control  :network-setup-control         -
pulseaudio             pulseaudio:client                   pulseaudio:service             -
snapd-control          console-conf:snapd-control          :snapd-control                 -
system-files           console-conf:run-console-conf       :system-files                  -
system-files           console-conf:var-log-console-conf   :system-files                  -

root@localhost:~# aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: vc4hdmi0 [vc4-hdmi-0], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: vc4hdmi1 [vc4-hdmi-1], device 0: MAI PCM i2s-hifi-0 [MAI PCM i2s-hifi-0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

root@localhost:~# pulse-server.pactl list sinks
Sink #0
	State: SUSPENDED
	Name: auto_null
	Description: Dummy Output
	Driver: module-null-sink.c
	Sample Specification: s16le 2ch 44100Hz
	Channel Map: front-left,front-right
	Owner Module: 15
	Mute: no
	Volume: front-left: 65536 / 100% / 0.00 dB,   front-right: 65536 / 100% / 0.00 dB
	        balance 0.00
	Base Volume: 65536 / 100% / 0.00 dB
	Monitor Source: auto_null.monitor
	Latency: 0 usec, configured 0 usec
	Flags: DECIBEL_VOLUME LATENCY 
	Properties:
		device.description = "Dummy Output"
		device.class = "abstract"
		device.icon_name = "audio-card"
	Formats:
		pcm

root@localhost:~# pulse-server.pactl list cards
<empty output>

ogra · January 23, 2025, 2:54pm

Yes, that is exactly what it is, it ships pulseaudio inside (like the pulseaudio snap does, just at a different version with different patch sets), they are the same thing in different variants … and indeed you don’t want to have both installed at the same time

Both snaps are based on core20 though (which corresponds to 20.04) and as you can see looking at the snapcraft.yaml they also build alsa-lib, alsa-plugins and alsa-ucm-conf from certain source tags, all this might just be too old …

gmattinson · January 23, 2025, 3:19pm

Would core20 also be too old for HDMI audio on a Pi 4? I did the following:

Same Ubuntu Core 24 image, with same gadget, and same changes mentioned originally in my post
Raspberry Pi 4 (instead of 5)
aplay -l lists vc4-hdmi-0, vc4-hdmi-1, and bcm2835 Headphones (headphones weren’t listed for Pi 5 since it doesn’t exist)
pulse-server.pactl list cards lists bcm2835 Headphones, but not the HDMI outputs…

Do you have a Pi 4, and do you know if pulse-server (or pulseaudio) works through the HDMI ports on a Pi 4?

ogra · January 23, 2025, 4:01pm

I must admit I don’t remember anymore (I built that snap in 2021), I know i tested and ran it on a Pi3 and 4 back then but can’t remember if I tested with a monitor (without speakers) or TV …

James-Carroll · January 23, 2025, 5:32pm

It’s worth potentially looking at Install pipewire on Linux | Snap Store - this will be supported in Ubuntu Core Desktop which ultimately is still Ubuntu Core. I’m not sure it’s ready for prime time yet but if the alternatives are literally functionless then a nicely confined beta is worth considering and I’m sure they could use the feedback if you have any to give!

Pipewire should be capable of providing Pulseaudio sockets.

gmattinson · January 23, 2025, 6:35pm

@James-Carroll, Thanks for the advice. I managed to get pipewire installed using:

sudo snap set system experimental.user-daemons=true
sudo snap install --edge pipewire

However, pactl list sinks is still outputting:

pa_context_connect() failed: Connection refused

I found a post recommending to use wpctl instead of pactl however wpctl is crashing even when simply running with the -h option to display help:

root@localhost:~# wpctl -h
W 18:30:48.338855            pw.loop ../src/pipewire/loop.c:67:pw_loop_new: 0xaaaace36a840: can't make support.system handle: No such file or directory
Segmentation fault (core dumped)

ogra · January 24, 2025, 8:25am

The pipewire snap is not ready for consumption on a plain Core without desktop session yet (on plain core it needs to be a system daemon as there are no user sessions (and on actual production devices that usually are managed via a fleet mgmt there aren’t even users at all)) …

Funnily I talked to @SergioCostas yesterday about this after taking a quick look at the packaging … on the packaging side it should be easy to achieve what is needed, but we need to do some tests to judge the behavior of pipewire in such a mode, this might take a bit of time…

gmattinson · January 24, 2025, 12:08pm

@ogra Thanks again for the insightful response. Please keep me posted on testing and when something might be available. I can wait some time.

The use case is a check-in kiosk. There is an RFID reader and a QT6 application. I simply want to hear a “beep” when an RFID card is read. I have it working on a regular Ubuntu Desktop 24.04 installation on a PC. Now it just needs to work on the Pi 5 with Ubuntu Core.

An alternate option for me might be to recompile QT with ALSA support, but I’d prefer to avoid compiling such a large package - I’m sure it will require a large dependency tree to achieve.

ogra · January 24, 2025, 12:21pm

Yeah, that would have been my suggestion for a quick solution, just have your app use alsa … especially in kiosk mode it is unlikely to have concurrent access of different apps to the audio device which is the actual purpose of running a sound daemon