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developer-guide.md 4.77 KiB

Aura Engine Development Guide

This page gives insights on extending Aura Engine internals or through the API.

AURA Componentes

AURA Engine as part of the AURA Radio Suite uses an modulear architecture based on a REST API. All external information is retrieved using JSON data-structures.

To get the basic architectural overview, visit the Aura Meta repository.

Starting development of engine can be quite tedious, as it requires all most all other AURA components to be up and running.

For example:

- Steering, to get the main incredient of an play-out engine: schedules (or "timeslots" in Steering terms), 
  which hold the actual information on playlists and their entries.
- Dashboard, to have a neat interface, being able to programm the schedules
- Tank, to get the references to audio files and other audio sources. Plus the actual files.

If you need to test and develop against the Engine's API you'll also need to get the engine-api project running.

For a start it's recommended to create a general aura project folder. In there you start cloning all the sub-projects. After having all the sub-projects configured, and verified that they are working, take a look at the AURA meta project.

There's a convenience script to start all of the three main dependencies (Steering, Dashboard, Tank) all at once:

    ~/code/aura/meta$ ./run.sh aura local

Engine Components

...TBD...

API

You can find the AURA API definition here: https://gitlab.servus.at/autoradio/meta/blob/master/api-definition.md

OpenAPI definition for Engine API: https://app.swaggerhub.com/apis/AURA-Engine/engine-api/

Engine Startup Phases

When you start Engine the following is happening:

  1. Python run.py: Initializes src/core/engine.py (The virtual mixer; class for remote-controlling Liquidsoap), Scheduler
  2. Python run.py: Start Liquidsoap.
  3. Liquidsoap: When Liquidsoap finished its startup, it creates a socket file as configured in socketdir of engine.ini.
  4. Python src/core/liquidsoap/client.py: Connects to that socket file.
  5. Python src/schedulung/scheduler.py: Continously loads schedules from the API endpoints, stores them in the local database and starts the playout as per the schedules.

More infos for debugging

Debugging Liquidsoap

Connect to Liquidsoap via Telnet

telnet 127.0.0.1 1234

List available commands

help

List all available channels

list

List all input channels connected to the mixer

mixer.input

Set the volume of mixer input 0 to 100%

mixer.volume 0 100

Push some audio file to the filesystem queue 0

in_filesystem_0.push /path/to/your/file.mp3

Tips on configuring the audo interface

Configure your audio device in the [soundcard] section of engine.ini.

You can configure up to five line IN and OUT stereo channels. Your hardware should support that. When you use JACK, you will see the additional elements popping up when viewing your connections (with e.g. Patchage).

Pulse Audio: When using Ubuntu, Pulse Audio is selected by default. This is convenient, as you won't have the need to adapt any Engine setting to get audio playing initially.

ALSA: When you use ALSA, you will have to play around with ALSA settings. In the folder ./src/liquidsoap is a scipt called alsa_settings_tester.liq. You can start it with 'liquidsoap -v --debug alsa_settings_tester.liq'. Changing and playing with settings may help you to find correct ALSA settings.

Jack Audio: Install the JACK daemon and GUI:

    sudo apt-get install jackd qjackctl

Please ensure to enable "realtime process priority" when installing JACK to keep latency low. Now, you are able to configure your hardware settings using following command:

    qjackctl

Next you need to install the JACK plugin for Liquidsoap:

sudo apt install \
    liquidsoap-plugin-jack

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