Working asound.conf settings for multichannel hdmi playback on headless linux

Plex Labs
1

Here are workarounds and settings I’ve found useful to get multichannel working out HDMI in plexamp

Pi3 (running raspberry pi os lite)

Edit the config.txt to include these lines

hdmi_force_hotplug=1

hdmi_force_edid_audio=1

hdmi_drive=2

change this line

dtoverlay=vc4-kms-v3d

to

dtoverlay=vc4-fkms-v3d

Copy and paste the below text to be your /etc/asound.conf

# Plexamp on Pi 3 - 5.1 HDMI with Center ↔ LFE swap

# Forces “Default” to be 6ch + remapped so Plexamp sends real 5.1

pcm.!default {

type plug

slave.pcm “remap51”

slave.channels 6 # ← THIS is what makes Plexamp see full 5.1 capability

}

pcm.remap51 {

type route

slave.pcm “hw:0,0” # the real multi-channel HDMI device

slave.channels 6

ttable {

0.0 1 # FL → FL

1.1 1 # FR → FR

2.3 1 # FC (input 2) → hardware FC (position 3)

3.2 1 # LFE (input 3) → hardware LFE (position 2)

4.4 1 # RL → RL

5.5 1 # RR → RR

}

}

HP EliteDesk 800G2 (running dietpi)

pcm.hdmi_raw {
type hw
card 0
device 3
}

pcm.routed8 {
type route
slave {
pcm “hdmi_raw”
channels 8
}
ttable {
0.0 1
1.1 1
2.4 1
3.5 1
4.6 1
5.7 1
6.6 0
7.7 0
}
}

pcm.!default {
type plug
slave.pcm “routed8”
slave.channels 8
}

ctl.!default {
type hw
card 0
}

I’ve not been having any luck with the Pi4 so far, but am hoping to crack that nut eventually.

2

Pi 4

Raspberry Pi Lite Bookworm

set hdmi to default with raspi-config

sudo nano /boot/firmware/config.txt

  1. Find the line that looks like this (it may be commented with #):

    text

    #dtoverlay=vc4-kms-v3d

    Change it to:

    text

    dtoverlay=vc4-fkms-v3d

  2. Add these lines at the end of the file (or uncomment if they exist):

    text

    hdmi_force_hotplug=1
hdmi_drive=2
hdmi_force_edid_audio=1

  3. Save (Ctrl+O → Enter → Ctrl+X), then reboot

I do not know if all those settings are valid or work in config, but this is what I did, so maybe with trial and error we can find some of the unnecessary.

sudo nano /etc/asound.conf

pcm.!default {
type plug
slave.pcm “remap51”
slave.channels 8
}

pcm.remap51 {
type route
slave.pcm “hw:0,0”
slave.channels 8
ttable {
0.0 1
1.1 1
2.4 1
3.5 1
4.2 1
5.3 1
6.6 0
7.7 0
}
}

ctl.!default {
type hw
card 0
}

save. reboot.

a headless plexamp install on the Pi4 set to output to default with stereo downmix disabled in both places (why are there 2 of these? this is poor practice - absolutely confusing to an end user who would reasonably expect this setting to take effect when set once) should work right now for 5.1 playback. I also set sampling rate to strict.

3

I don’t know what changed, but my Pi4 process here is no longer working. Digging a bit, but I’ll probably give up soon.

4

My Pi4 is still completely broken for plexamp, I am not sure what went wrong there.

Needed to spin up another HP mini PC, this time with debian, and the above configuration that worked on diet-pi on the PC didn’t work. This one below does.

pcm.routed8 {
type route
slave {
pcm {
type hw
card 0
device 3
}
channels 8
}
ttable {
0.0 1
1.1 1
2.4 1
3.5 1
4.6 1
5.7 1
6.6 0
7.7 0
}
}

pcm.!default {
type plug
slave.pcm “routed8”
slave.channels 8
}

ctl.!default {
type hw
card 0
}