JACK-Client 0.4.1

Requirements

Python:

Of course, you’ll need Python. Any version where CFFI (see below) is supported should work. If you don’t have Python installed yet, you should get one of the distributions which already include CFFI and NumPy (and many other useful things), e.g. Anaconda or WinPython.

pip/setuptools:

Those are needed for the installation of the Python module and its dependencies. Most systems will have these installed already, but if not, you should install it with your package manager or you can download and install pip and setuptools as described on the pip installation page. If you happen to have pip but not setuptools, use this command:

pip install setuptools --user

CFFI:

The C Foreign Function Interface for Python is used to access the C-API of the JACK library from within Python. It supports CPython 2.6, 2.7, 3.x; and is distributed with PyPy 2.0 beta2 or later. You should install it with your package manager (if it’s not installed already), or you can get it with:

pip install cffi --user

JACK library:

The JACK library must be installed on your system (and CFFI must be able to find it). Again, you should use your package manager to install it. Make sure you install the JACK daemon (called jackd). This will also install the JACK library package. If you don’t have a package manager, you can try one of the binary installers from the JACK download page. If you prefer, you can of course also download the sources and compile everything locally.

NumPy (optional):

NumPy is only needed if you want to access the input and output buffers in the process callback as NumPy arrays. The only place where NumPy is needed is jack.OwnPort.get_array(). If you need NumPy, you should install it with your package manager or use a Python distribution that already includes NumPy (see above). Installing NumPy with pip requires a compiler and several additional libraries and is therefore not recommended for beginners.

Installation

Once you have installed the above-mentioned dependencies, you can use pip to download and install the latest release with a single command:

pip install JACK-Client --user

If you want to install it system-wide for all users (assuming you have the necessary rights), you can just drop the --user option.

To un-install, use:

pip uninstall JACK-Client

If you want to avoid installation altogether, you can simply copy jack.py to your working directory (or to any directory in your Python path).

Usage

First, import the module:

>>> import jack

Then, you most likely want to create a new jack.Client:

>>> client = jack.Client("MyGreatClient")

You probably want to create some audio input and output ports, too:

>>> client.inports.register("input_1")
jack.OwnPort('MyGreatClient:input_1')
>>> client.outports.register("output_1")
jack.OwnPort('MyGreatClient:output_1')

As you can see, these functions return the newly created port. If you want, you can save it for later:

>>> in2 = client.inports.register("input_2")
>>> out2 = client.outports.register("output_2")

To see what you can do with the returned objects, have a look at the documentation of the class jack.OwnPort.

In case you forgot, you should remind yourself about the ports you just created:

>>> client.inports
[jack.OwnPort('MyGreatClient:input_1'), jack.OwnPort('MyGreatClient:input_2')]
>>> client.outports
[jack.OwnPort('MyGreatClient:output_1'), jack.OwnPort('MyGreatClient:output_2')]

Have a look at the documentation of the class jack.Ports to get more detailed information about these lists of ports.

If you have selected an appropriate driver in your JACK settings, you can also create MIDI ports:

>>> client.midi_inports.register("midi_in")
jack.OwnMidiPort('MyGreatClient:midi_in')
>>> client.midi_outports.register("midi_out")
jack.OwnMidiPort('MyGreatClient:midi_out')

You can check what other JACK ports are available (your output may be different):

>>> client.get_ports()  # doctest: +SKIP
[jack.Port('system:capture_1'),
 jack.Port('system:capture_2'),
 jack.Port('system:playback_1'),
 jack.Port('system:playback_2'),
 jack.MidiPort('system:midi_capture_1'),
 jack.MidiPort('system:midi_playback_1'),
 jack.OwnPort('MyGreatClient:input_1'),
 jack.OwnPort('MyGreatClient:output_1'),
 jack.OwnPort('MyGreatClient:input_2'),
 jack.OwnPort('MyGreatClient:output_2'),
 jack.OwnMidiPort('MyGreatClient:midi_in'),
 jack.OwnMidiPort('MyGreatClient:midi_out')]

Note that the ports you created yourself are of type jack.OwnPort and jack.OwnMidiPort, while other ports are merely of type jack.Port and jack.MidiPort, respectively.

You can also be more specific when looking for ports:

>>> client.get_ports(is_audio=True, is_output=True, is_physical=True)
[jack.Port('system:capture_1'), jack.Port('system:capture_2')]

You can even use regular expressions to search for ports:

>>> client.get_ports("Great.*2$")
[jack.OwnPort('MyGreatClient:input_2'), jack.OwnPort('MyGreatClient:output_2')]

If you want, you can also set all kinds of callback functions for your client. For details see the documentation for the class jack.Client and the example applications in the examples/ directory.

Once you are ready to run, you should activate your client:

>>> client.activate()

As soon as the client is activated, you can make connections (this isn’t possible before activating the client):

>>> client.connect("system:capture_1", "MyGreatClient:input_1")
>>> client.connect("MyGreatClient:output_1", "system:playback_1")

You can also use the port objects from before instead of port names:

>>> client.connect(out2, "system:playback_2")
>>> in2.connect("system:capture_2")

Use jack.Client.get_all_connections() to find out which other ports are connected to a given port. If you own the port, you can also use jack.OwnPort.connections.

>>> client.get_all_connections("system:playback_1")
[jack.OwnPort('MyGreatClient:output_1')]
>>> out2.connections
[jack.Port('system:playback_2')]

Of course you can also disconnect ports, there are again several possibilities:

>>> client.disconnect("system:capture_1", "MyGreatClient:input_1")
>>> client.disconnect(out2, "system:playback_2")
>>> in2.disconnect()  # disconnect all connections with in2

If you don’t need your ports anymore, you can un-register them:

>>> in2.unregister()
>>> client.outports.clear()  # unregister all audio output ports

Finally, you can de-activate your JACK client and close it:

>>> client.deactivate()
>>> client.close()