A Julia MIDI Mixer / Player with an OpenGL based GUI
Author JuliaMusic
32 Stars
Updated Last
2 Years Ago
Started In
March 2017


Mplay is a full functional MIDI player written in pure Julia. It reads Standard MIDI Files (SMF) and sends them to MIDI devices (or software synthesizers) while giving visual feedback.

This current version runs on macOS and Windows. Mplay has been tested with Julia 1.5 (or later) and GLFW 3.3.

macOS and Windows systems come with a builtin software synthesizer (Apple DLS SoftSynth, Microsoft GS Wavetable SW Synth). On those systems Mplay runs out of the box. However, best results can be achieved with the Roland Sound Canvas VA software synthesizer:



  • Full functional MIDI player
  • Mixer with mute and solo options
  • Ability to change channel parameters (delay, chorus, reverb, pan)
  • Volume sliders
  • Change GM instrument sounds
  • MIDI VU meter
  • Show note, chord and lyrics information
  • Change key, tempo
  • Transport controls
  • Keyboard shortcuts
  • Support for Roland sound maps (SC-88 Pro, SC-88, and SC-55)
Key Action
a un-mute all channels
b/B toggle/solo bass
d/D toggle/solo drums
g/G toggle/solo guitar(s)
k/K toggle/solo keyboard(s)
1234567890!@#$%^ toggle channel 1-16
-/+ decrease/increase tempo
SPACE stop/resume song
TAB select next channel
> < transpose up/down, or
next/previous GM instrument
(if a channel is selected)
ESC quit Mplay



On macOS and Windows systems Mplay comes as a self-contained package with its own wrappers for GLFW and OpenGL as well as the required run-time libraries for the GUI and Midi subsystems.


using Mplay
mplay(<path to midi file>)

Of course, you can also use Mplay from the command line, e.g.:

julia Mplay.jl <path to midi file>


Mplay has no innovative features - the main focus is on simplicity and ease of use. It uses texture blitting to guarantee highest refresh rates. That's why it responds in real-time in the order of milliseconds, both to user interactions and MIDI events.

If, for any reason, the contained MIDI run-time doesn't work, you can build your own binaries:


cc -shared -arch arm64 -arch x86_64 -o libmidi.dylib libmidi.c \
   -framework CoreMIDI -framework CoreAudio -framework AudioUnit \
   -framework AudioToolbox -framework Cocoa
cc -shared -arch arm64 -arch x86_64 -o libconsole.dylib libconsole.c


cl /c libmidi.c
link /out:libmidi.dll -dll libmidi.obj winmm.lib
cl /c libconsole.c
link /out:libconsole.dll -dll libconsole.obj


cc -shared -fPIC -o libmidi.c -lasound
cc -shared -fPIC -o libconsole.c

There is also a startup script in the src directory which you can symlink to simplify the use of Mplay, e.g.

ln -s ${HOME}/Mplay.jl/src/ /opt/bin/Mplay

With the Mplay command you can not only select the desired user interface, but also specify the MIDI device. For example, under macOS the current version offers the possibility to redirect the MIDI output to the Roland Sound Canvas VA plugin (--device=scva) - if installed - as an alternative to the default Apple DLS Music Device.

% Mplay -h
Mplay [-h|--help] [--device=midi-device] [--gui] midi-file

The text user interface is now enabled by default.


How to use Mplay with Timidity++ (on Linux)

Before you start Timidity++, you have to create a virtual MIDI device:

% sudo modprobe snd-virmidi
% timidity -iA
TiMidity starting in ALSA server mode
Opening sequencer port: 128:0 128:1 128:2 128:3

Then, in a second console window, you can setup the MIDI connections and use Mplay with the proper device specification, e.g.:

% aconnect 20:0 128:0
% aconnect -l
client 20: 'Virtual Raw MIDI 1-0' [type=kernel,card=1]
    0 'VirMIDI 1-0     '
	Connecting To: 128:0
client 128: 'TiMidity' [type=user,pid=...]
    0 'TiMidity port 0 '
	Connected From: 20:0
% Mplay --device=hw:1,0 <midi-file>

Please keep in mind: The client/device IDs on your system may differ from those shown here depending on the configuration of your Audio/MIDI interface(s).