Using Sponge and the Sponge Remote Mobile App as a Remote Hi-Fi Music Player

30 Aug 2020 - Marcin Paś

If you are not familiar with Sponge and the Sponge Remote mobile app, please read the Getting Started with Sponge and the Sponge Remote Mobile App article first.

After reading this article you will learn:

How to run the Sponge Music Player Daemon (MPD) Service in Docker on Raspberry Pi.
How to connect to the service using the Sponge Remote mobile app.
How to use the Sponge Remote mobile app as a remote music player.

1. What you need

About 20 minutes (depending on your current Raspberry Pi configuration).
Raspberry Pi 4 with a Hi-Fi system hardware (DAC, speakers, etc.).
Micro SD card.
An Android phone or tablet.

2. Introduction

The Sponge Music Player Daemon (MPD) Service publishes a basic set of Sponge actions that enable you to use the Sponge Remote mobile app as a remote music player.

The service runs in Docker on Raspberry Pi with an already configured MPD. There is a number of Linux distributions for Raspberry Pi that provide well configured music player features. For this article the moOde audio player has been chosen.

The architecture of this solution is: Raspberry Pi with the MPD server (running in the moOde audio distribution) and Docker containing the Sponge MPD Service.

Although the Sponge MPD Service may seem to be only for entertainment, it is built on the same principles as an IoT device. In fact, the Sponge MPD Service can be seen as an IoT device that has as a set of sensors (that generate MPD events just like playing started/paused, song changed, volume changed) and actuators (MPD actions just like play/pause, play a song from the playlist, change volume).

One of the aims of the Sponge MPD Service is to showcase the ability of Sponge to publish a set of commandline tool invocations as a Remote API and use it in a mobile application. It is not a replacement for existing MPD clients available for mobile devices because they connect to an MPD server directly. The architecture shown in this article introduces an additional layer between the MPD server and the GUI MPD client (the Sponge Remote mobile app) that can have a noticable impact on the performance.

3. Install the moOde audio player on your Raspberry Pi

Download the moOde audio player for Raspberry Pi.
The download is a ready-to-use ISO image. Write it to a micro SD card, boot up your Raspberry Pi and then view the Setup guide to get started.

4. Install Docker on your Raspberry Pi

Connect to the Raspberry Pi via SSH as the pi user.

Install and configure Docker on your Raspberry Pi.

sudo curl -fsSL https://get.docker.com -o get-docker.sh && sh get-docker.sh
sudo usermod -aG docker pi

Relogin.

5. Run the Sponge MPD Service

Run the Sponge MPD Service by typing the following commands.
```
docker pull openksavi/sponge-mpd

docker run --name sponge-mpd -d --restart always --network=host openksavi/sponge-mpd \
-Dsponge.remoteApiServer.serviceDiscoveryUrl="http://$(hostname -I | awk '{print $1}'):1836"
```
The Docker image openksavi/sponge-mpd contains the Sponge MPD Service.

Setting the sponge.remoteApiServer.serviceDiscoveryUrl property allows the Sponge Remote mobile app to automatically find this service on the local network. If you want to change the service name, provide the sponge.remoteApiServer.name property as well, e.g. -Dsponge.remoteApiServer.name="Docker MPD".
Check the Sponge MPD service logs.
```
docker logs sponge-mpd -f
```

Optionally, if you have a Musixmatch API key, you can configure the service to access song lyrics by adding -DmusixmatchApiKey=YOUR_MUSIXMATCH_API_KEY to the docker run command line. Song lyrics will be shown in the Sponge Remote app.

6. Open the Sponge Remote mobile app and connect to the service

Open the Sponge Remote mobile app on your Android device.

Tap to create a new connection to the MPD service.

There are two ways to add new connections:

By service discovery - select the Find new nearby services menu item. The service discovery may not work in Docker or would require additional configuration in some environments.
By creating a connection manually - tap the plus sign icon, fill in the connection name, Sponge address (the Raspberry Pi IP address) and tap the OK button.

In the Connections page tap the new connection to activate it.

You are navigated back to the Actions page.

7. Open the remote music player

Now you can see the Sponge actions related to the Music Player Daemon in the MPD tab.

Tap the Player action to open it.

Take a look at the available context actions in the menu.

8. Explore player context actions

The Playlist action.

The Lyrics action.

The MPD status action.

9. How does it work?

The Sponge MPD service uses the mpc client commandline to communicate with the MPD server. For performance reasons the Sponge MPD service should be installed on the same machine that runs the MPD server just like it is shown in this article.

Each action argument modification in the player submits the respective argument to the service. MPD events cause refreshing of provided action arguments.

For more details see the source codes of the sponge-kb-mpd-mpc knowledge base.

10. Summary

Congratulations! Now you are familiar with using Sponge and the Sponge Remote mobile app as a remote Hi-Fi music player.

One interesting fact is that you can use the same Sponge Remote mobile app to connect to such diverse Sponge services as for example a remote music player. In this article a predefined Sponge service has been presented. For more information on creating your own services see the Creating a New Service with Sponge and the Sponge Remote Mobile App article.

In the forthcoming articles about Sponge you will learn how Sponge with the Sponge Remote mobile app can help you with your other daily activities (both personal and professional).

Link to the Medium article.