Audio Servers

The JAudioLibs AudioServer API provides a Java callback-based API for audio and DSP programming, loosely inspired by PortAudio. Implementations based on JavaSound and JACK (using JAudioLibs' JNAJack) can also be found here. Additional implementation may be found elsewhere.

The AudioServer API was initially developed for use in PraxisLIVE, but has found its way into a variety of other applications. Using the AudioServer API provides an application with the ability to easily switch between audio backends at runtime, and can also make working with JavaSound a little easier.

Usage

The AudioServer API is designed to be as simple as possible to use. All an application needs to do is provide an implementation of the AudioClient interface, and its three methods – configure(), process() and shutdown(). This AudioClient implementation can then be passed to any AudioServer to run.

The configure() method is called prior to any call to process(). It provides an AudioConfiguration object with details of sample rate, buffer size, channels, etc. When requesting an AudioServer implementation, an AudioConfiguration object is also used to request configuration. Depending on the server implementation, the passed back configuration may not match!

All audio processing is done through the process() callback. The client will be provided with lists of FloatBuffer. These may be direct pointers to natively allocated audio buffers. The code inside process() should never block, and never do anything other than necessary audio processing - it's going to be called hundreds of times a second.

Applications should not use audio server implementations directly, but use the Java ServiceLoader mechanism to lookup available server implementations at runtime.

Check out the examples repository for some simple examples of using the API directly. In particular the SineAudioClient

The JAudioLibs Pipes library provides an audio routing and unit generator library built on top of the AudioServer API that may be useful for many applications.

Arbitrary extensions

Both the AudioConfiguration and AudioServerProvider classes provide a way of passing across or searching for arbitrary extensions.

public <T> T find(Class<T> type)
public Iterable<T> findAll(Class<T> type)

eg. use this feature to lookup devices if the audio server provides more than one.

for (AudioServerProvider provider : ServiceLoader.load(AudioServerProvider.class)) {
  System.out.println("Found library : " + provider.getLibraryName());
    System.out.println("==============================================");
    System.out.println("Devices");
    System.out.println("----------------------------------------------");
    for (Device dev : provider.findAll(Device.class)) {
        System.out.println(dev.getName() + 
        " (inputs: " + dev.getMaxInputChannels() +
        ", outputs: " + dev.getMaxOutputChannels() + ")");

    }
}

A Device can be chosen and passed into the constructor for the AudioConfiguration used to create an audio server in order to choose that device for playback. Note that on some OS, two devices (one for input, one for output) may need to be used.

Additional extensions include ClientID and Connections that are primarily of use when use to control the JACK server implementation.