RtMidi (Default, Recommended)

Name: mido.backends.rtmidi

Resources:

• python-rtmidi Python Library

• RtMidi C Library

The RtMidi backend is a thin wrapper around python-rtmidi.

Features

• callbacks

• true blocking receive() in Python 3 (using a callback and a queue)

• virtual ports (Except on Microsoft Windows)

• ports can be opened multiple times, each will receive a copy of all messages

• a client name can be specified when opening a virtual port

• sends but doesn’t receive active sensing (By default)

• port list is always up to date

• all methods but close() are thread safe

Port Names (Linux/ALSA)

When you’re using Linux/ALSA the port names include client name and ALSA client and port numbers, for example:

>>> mido.get_output_names()
['TiMidity:TiMidity port 0 128:0']

The ALSA client and port numbers (”128:0” in this case) can change from session to session, making it hard to hard code port names or use them in configuration files.

To get around this the RtMidi backend allows you to leave out the port number of port number and client names. These lines will all open the same port as above:

mido.open_output('TiMidity port 0')

mido.open_output('TiMidity:TiMidity port 0')

mido.open_output('TiMidity:TiMidity port 0 128:0')

There is currently no way to list ports without port number or client name. This can be added in a future version of there is demand for it and a suitable API is found.

Virtual Ports

RtMidi is the only backend that can create virtual ports:

>>> port = mido.open_input('New Port', virtual=True)
>>> port
<open input 'New Port' (RtMidi/LINUX_ALSA)>

Other applications can now connect to this port. (One oddity is that, at least in Linux, RtMidi can’t see its own virtual ports, while PortMidi can see them.)

Note

Virtual Ports are not available under Microsoft Windows. An alternative is to use third party software such as Tobias Erichsen’s loopMIDI.

Client Name

Added in version 1.2.

You can specify a client name for the port:

>>> port = mido.open_input('New Port', client_name='My Client')

This requires python-rtmidi >= 1.0rc1. If client_name is passed the port will be a virtual port.

Note

Unfortunately, at least with ALSA, opening two ports with the same client_name creates two clients with the same name instead of one client with two ports.

There are a couple of problems with port names in Linux. First, RtMidi can’t see some software ports such as amSynth MIDI IN. PortMidi uses the same ALSA sequencer API, so this is problem in RtMidi.

Second, in some versions of RtMidi ports are named inconsistently. For example, the input port ‘Midi Through 14:0’ has a corresponding output named ‘Midi Through:0’. Unless this was intended, it is a bug in RtMidi’s ALSA implementation.

Choosing an API

The RtMidi library can be compiled with support for more than one API.

To get a list of all available APIs at runtime:

>>> mido.backend.module.get_api_names()
['LINUX_ALSA', 'UNIX_JACK']

You can select the API by adding it after the module name, either in the environment variable:

$ export MIDO_BACKEND=mido.backends.rtmidi/LINUX_ALSA
$ export MIDO_BACKEND=mido.backends.rtmidi/UNIX_JACK

or within the program using one of these:

>>> mido.set_backend('mido.backends.rtmidi/LINUX_ALSA')
>>> mido.backend
<backend mido.backends.rtmidi/LINUX_ALSA (not loaded)>

>>> mido.Backend('mido.backends.rtmidi/UNIX_JACK')
<backend mido.backends.rtmidi/UNIX_JACK (not loaded)>

This allows you to, for example, use both ALSA and JACK ports in the same program.