Can't get audio over HDMI on rpi

[DockDuckDaisy]

I want to run shairport-sync on an rpi 3B and output the audio over HDMI.
I have tried for so long to solve this, but I am at the end of my rope. Can anyone help?

My RPi 3B has been running shairport-sync for many years. At one point something broke in an update and shairport-sync became unstable. It would play audio but crash after a short time whenever I tried to use it. I did a clean install of the OS, switching to a lite version with no desktop, and ALSA as the backend. Shairport-sync works fine over the headphone jack, but when I switch to HDMI it refuses to work. Speakertest and mpv both successfully output over HDMI, so it is not a problem with the hardware or signal chain.

Shairport-sync over HDMI starts and runs, but as soon as I connect from a source device, the process crashes.

Verbose output of the failure:

0.006417031 "audio_alsa.c:551" *fatal error: audio_alsa: Could not automatically set the output format for device "hw:vc4hdmi": Invalid argument
0.000221927 "rtsp.c:531" Connection 1: cancelled.
101.700378711 "shairport.c:1728" emergency exit

sps-alsa-explorer tells me:

Device Full Name:    "hw:vc4hdmi"
Short Name:          "hw:1"
Shairport Sync can not use this device.

This seems significant... but in all my searching, I only find dead ends.

shairport-sync -V

4.3.2-2-g165431a8-AirPlay2-smi10-OpenSSL-Avahi-ALSA-soxr-sysconfdir:/etc

Other details:
Raspberry Pi 3B
Raspberry Pi OS (Legacy) Lite - Bullseye
HDMI
ALSA

[mikebrady]

Thanks for the post. Would this discussion be relevant at all?

Also, just wondering if the device you plug in to the HDMI port has changed at all?

[DockDuckDaisy]

Hi, thank you so much for replying!
My hardware is unchanged, same old devices all the way.

I already found and followed the linked thread. But alas, it is a dead end for me. It mentions "Shairport Sync can not use this device.", which seems like the best clue.

"dtparam=audio=on" will turn on the audio card that powers headphone jack, and load it's driver. The HDMI is unaffected by this as far as I can tell. I am able to produce audio over HDMI using speakertest/mpv with or without that parameter enabled. And the behaviour of shairport-sync is the same (if directed to use the hdmi card).

I have also found and followed the common advice to set these parameters in /boot/config.txt
hdmi_group=1
hdmi_mode=1
hdmi_drive=2
Those seem to be required, but my problem persists.

[DockDuckDaisy]

Hi, not sure if you saw my followup reply here?

If HDMI out on Rpi using ALSA is not supported, what should I switch to?

[mikebrady]

Apologies, I missed this. Let me come back on this.

[mikebrady]

Thanks again for the reminder.

(Some time ago, possibly a year or so, it seems as if drivers were changed -- e.g. see a discussion here -- and this may be the cause of the difficulty.)

So, just playing about with a Raspberry Pi 3B on the latest version of Raspberry Pi OS.
In this case, the /boot/config.txt is untouched: there no changes to the dtparam=audio=on and none of those hdmi_group=... settings have been added.

Raspberry Pi 3 Model B Rev 1.2
Linux RaspberryPi3B 6.6.28+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.6.28-1+rpt1 (2024-04-22) aarch64 GNU/Linux

Now, if a HDMI cable is plugged into the Pi and connected at the other end to the output device (e.g. a TV) with is switched on, then by substituting hdmi for hw in the alsa output_device setting, it works as an output device. In your case, you would use output_device = "hdmi:1"; instead of output_device = "hw:1";.

If the HDMI cable is disconnected, it stops working. When plugged back in, it takes a few seconds for it to be recognised and it works again.

Would you be kind enough to try that and see if it works, please? You should set the log_verbosity to 1 and enable statistics (both in the diagnostics section of the configuration file).

I'm afraid the sps-alsa-explore tool doesn't check for devices with thehdmi: prefix at present, but I'll post an update to it soon.

In my case, it reports the the HDMI output a suitable mixer called "PCM" but I don't know if that's specific to the device that the HDMI cable is connected to... Might be worth trying...

[DockDuckDaisy]

Preliminary result: Yey!

I reinstalled a fresh version of shairport-sync (following the build instructions) and switched to development branch.
Then I changed the config to enable logging and statistics, as well as output_device = "hdmi:vc4hdmi

It now works! I get audio out through hdmi.

I am running rpi3B--hdmi-->reciever (there is a TV connected, but it is speakerless, and unpowered most of the time)

Hot unplug and reconnect of hdmi at the rpi3b end does not break anything. Audio resumes after plugging in.

My /boot/config.txt is still modified as before, although I did set dtparam=audio=on before starting the experiment.

I will let this run for a while to see that it keeps going, but so far so good!
Do you still want logs if everything is working fine?

[mikebrady]

That’s great news. In fact, thanks to your prompting, I’ve learned quite a bit. Working through this, the help section of Shairport Sync has been corrected as well as sps-alsa-explore.

There’s no real need for the logs now, thanks. But if things go wrong, of course…

[mikebrady]

So I just pushed an update to sps-alsa-explore in the experimental branch. It should detect HDMI devices and mixers properly. If you got a chance to try it and see if it's working for you, it would be appreciated.

[DockDuckDaisy]

My git-fu is weak, but I got the experimental sps-alsa-explore set up. It does indeed provide a different result, and seems to be properly detecting the hdmi. I will proceed to check the other posts you made and reply to them as well.

Device Full Name: "hdmi:vc4hdmi"
Short Name: "hdmi:0"
This device seems suitable for use with Shairport Sync.
Possible mixers: "PCM",0 Range: 51.00 dB
The following rate and format would be chosen by Shairport Sync in "auto" mode:
Rate Format
44100 S32_LE

In case it matters, here is the tag list.
1.0
1.0.1
1.0.3d3
1.0.3d4
1.1
1.2
1.2-dev
1.2.1
1.2.1-dev

[mikebrady]

You've done well, thanks!

So, it's worth trying Shairport Sync now with the output_device = "hdmi:vc4hdmi".

AFAIK that mixer called PCM doesn't do anything, so best leave the mixer_control_name commented out...

[DockDuckDaisy]

Thank you! I will test it out and report back.

[mikebrady]

Thanks. Just FYI I've noticed that the development and master versions of Shairport Sync can't access that PCM mixer. I'll update the development version to be able to see it in the next day or so, but AFAIK it doesn't seem to be a volume control anyway...

[Tiefflieger]

Nothing was working to get HDMI Audio Output to work on my raspberry pi 4 with the docker options. So I investigated on system level to see if the HDMI audio output was possible. I made changes to the /boot/config.txt as mentioned here: Enable HDMI Sound

# uncomment to force a specific HDMI mode (this will force VGA)
hdmi_group=1
hdmi_mode=1
# uncomment to force HDMI mode rather than DVI. This can make audio work in DMT (computer monitor) modes
hdmi_drive=2

I used this command, my HDMI is connected to the second port:
docker run -d --restart unless-stopped --net host --device /dev/snd mikebrady/shairport-sync -a Airpi -- -d hdmi:2

[mikebrady]

Thanks for this!