IoT : How I added AirPlay 2 support to BalenaSound on a Sunday Afternoon

I use Balena Sound running on a Raspberry Pi plugged in a DAC at home, as an AirPlay receiver.
In layman's terms: I play my music through the WiFi on a non-intelligent hifi system using a Raspberry Pi.

Balena Sound is a mix of two great open-source projects:

• BalenaOS, which is a portable and reliable operating system targetting embedded devices.
• Shairport sync, an open-source implementation of an AirPlay client, providing AirPlay 2 support since a few weeks now.

Balena Sound uses an outdated Shairport version, and I wanted to check how hard it would be to upgrade to the current release, bringing AirPlay 2 to my modest multiroom setup.

Note that I have no links with Balena. I am just a IoT hobbyist enjoying a few connected devices. I like to experiment, and Balena offers a few other interesting pre-built OS images, to read from sensors or to create a live stream.
I know of a few free software alternatives to Balena, but I did not find enough time yet to invest into such alternatives.

Where to start

I did not know where to start, so I simply asked for help and got some quickly in the GitHub issue queue. Documentation is pretty straightforward:

1. Make some changes to a balena project of your choice.
2. Install Balena CLI.
3. Push and deploy these changes.

I blindly started by bumping the shairport version in Balena Dockerfile.
Using the Balena CLI, you can easily publish your changes to your fleet by typing balena push balena-sound -s . . It will:

1. Build the containers.
2. Push it to your devices.
3. Restart those containers on your devices.

It takes around a minute to build an around a minute to publish. Not a big deal if you have some time to kill on a Sunday 😅

As expected, it did not work, with the error below:

airplay  fatal error: Can't access NQPTP! Is it installed and running?

Debug

If you know Docker, debugging can be done locally using docker compose.
A docker-compose.yml config file is provided with the project, allowing you to build and run docker images locally. However if you don't, you can simply deploy your changes and inspect the logs through balena dashboard on a running balena device build and tweak the Dockerfile accordingly.
I did both as I needed to test this on my raspberry pi.
In the end I stopped building locally as deploying on Balena cloud was not much longer, and provided a great developer experience : you get a running software on a remote device after a few minutes, with easy to browse logs.

In my case, the error above was quite self explanatory : NQPTP - that is required for Shairport Sync v4.1 to run properly - is not running. It appears that even if the shairport sync docker image has NQPTP built and installed, it does not run by default with the script set in the entrypoint previously used by Balena Sound.

The fix and the changes are visible in this pull request. They were quickly approved and are now part of Balena Sound 🥳.

Conclusion

Thanks to the help of the community (maggie44 especially), a simple CLI and a nice platform, I was able to publish a new feature to Balena Sound, test it on my own device and release as a test version for others to try it out, all this during a Sunday afternoon.
I don't think I experienced such a nice developer experience on a stack I just discovered.

However, if you know nothing about Docker, it might not be the best platform for you, or it might be the time to learn a few things about it as it seems to be quite popular among IoT projects.