Multiple containers with separate audio outputs

General
1

I’m new to Docker but already love it. I spun up a home server on Ubuntu Xenial on an x86 box. My setup is home automation centric. I’ve got openHAB, mosquitto, frontail, and Shinobi running so far.

My question: how hard is it to configure multiple containers with separate audio outputs? I was planning to connect several USB audio output dongles and map each one to a container. I’d like openHAB to have its own output and also run a squeezebox container and a shairport sync container.

My backup is to use a few Raspberry Pi’s but I’ve really been loving the simplicity of getting everything centralized on one box.

2

Hi,

This is probably do-able for you, using the --device flag in the run command. For example

$ docker run --rm -t -i --device=/dev/ttyUSB0 ubuntu bash

So long as each dongle has a unique device, you can attach each device to its respective container at run time. USB devices can be tricky: device names are often assigned at boot time, and often don’t persist through reboots.

3

Sounds good, I’ll try it!

Do you know if I need to configure/install ALSA or something similar in the containers, or is it sufficient to install it on the host?

4

I don’t know about ALSA and containers; I’ve never personally tried multiplexing audio across multiple containers, and don’t have a setup to try anything. I did find this thread in StackOverflow that suggests some changes/reconfiguration is required to make it work. It’s quite an old thread, and again, I haven’t personally tried it, so YMMV, caveats apply, try at your own risk, etc. https://stackoverflow.com/questions/28985714/run-apps-using-audio-in-a-docker-container

5

Thanks @bryceryan for pointing me in the right direction!

I got it all working, and wanted to briefly explain for the benefit of someone who might find this thread. I tried quite a few steps through trial and error, but I believe these are the general steps to follow.

Before anything else I installed ALSA on the host machine. I believe it would be impossible to do this inside a container.

Then I got shairport sync working using the knapoc/shairport-sync image. My USB devices didn’t show up under /dev/tty, so I determined that I would need to define their locations elsewhere. I loaded the shairport image using the -v "/opt/shairport/shairport-sync.conf:/usr/local/etc/shairport-sync.conf" \ option, and configured the shairport-sync.conf file to look for the appropriate output device. If you find yourself stuck at this point, utilize the documentation for the shairport-sync general package. I also had to set the --device=/dev/snd:/dev/snd \ option so the container had access to audio.

For reference, my shairport run command:
sudo docker run \ -d \ --name=shairport \ --restart=always \ --net=host \ --device=/dev/snd:/dev/snd \ -v "/opt/shairport/shairport-sync.conf:/usr/local/etc/shairport-sync.conf" \ knapoc/shairport-sync

I wanted a squeezebox and for openHAB to be able to independently make announcements. Since openHAB uses the audio settings of its host machine and configuring the openHAB image for audio output looked tedious, I decided instead to spin up two squeezebox players - one for general audio playback and one just for openHAB alerting. openHAB supports piping audio to a squeezebox player.

My two squeezebox instances:
sudo docker run \ -d \ --name=squeezelite1 \ --restart=always \ --device=/dev/snd/ \ -v /opt/squeezelite/i1:/config \ -e USER_ID=65534 \ -e GROUP_ID=100 \ -e UMASK=0002 \ -e PLAYER=squeezelite1 \ -e OUTPUT_DEVICE=front:CARD=Device,DEV=0 \ -e MAC_ADDRESS=redacted \ aschamberger/squeezelite

sudo docker run \ -d \ --name=squeezelite2 \ --restart=always \ --device=/dev/snd/ \ -v /opt/squeezelite/i2:/config \ -e USER_ID=65534 \ -e GROUP_ID=100 \ -e UMASK=0002 \ -e PLAYER=squeezelite2 \ -e OUTPUT_DEVICE=front:CARD=Intel,DEV=0 \ -e MAC_ADDRESS=redacted \ aschamberger/squeezelite

Again, I used the non-docker squeezelite documentation for hints on how to determine how to define the audio devices. I accessed the bash environment inside the containers using docker exec -ti containerID /bin/bash then used the appropriate commands, as listed in the documentation for the software, to display the available audio devices.

I ended up using the built-in sound card and two USB audio dongles, and they work flawlessly! I paired them with a MonoPrice 6 zone amp, and hooked the audio outputs up to three discrete outputs.