Enabling MIDI editors to play MIDI files on Linux (without an external musical device)

Question

I cannot enable MIDI files to be played on Linux in editors such as Qtractor or MidiEditor. Why is it not working when VLC can play these MIDI files?

Details:

I was able to make VLC play .mid files on Ubuntu 22.04 LTS by installing:

sudo apt-get install fluid-soundfont-gm fluid-soundfont-gs
sudo apt-get install vlc-plugin-fluidsynth 

However, I am not able to make them play on some MIDI editors like MidiEditor and Qtractor. The problem is always the same - It cannot find the MIDI output device. I do not want to use any external hardware output device. Instead, I wish to use the software synthesizer (fluidsynth) in the same way as VLC uses it.

For example, with Qtractor I got this error

The audio/MIDI engine could not be initialized. Make sure the JACK audio server (jackd) and/or the ALSA Sequencer kernel module (snd-seq-midi) are up and running and then restart the session.

I was trying to solve it by installing qsynth or qjackctl as described here. But for some reason I don't understand I cannot. Terminal output:

myComputer:~/SW$ sudo apt install qsynth

Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 midieditor : Depends: qtbase5-dev but it is not going to be installed
              Depends: qtdeclarative5-dev but it is not going to be installed
              Depends: libqt5webkit5-dev but it is not going to be installed
              Depends: libsqlite3-dev but it is not going to be installed
              Depends: qt5-default but it is not installable
              Depends: qtmultimedia5-dev but it is not going to be installed
              Depends: qttools5-dev-tools
              Depends: libqt5multimedia5-plugins but it is not going to be installed
              Depends: gstreamer1.0-plugins-bad but it is not going to be installed
              Depends: gstreamer1.0-doc but it is not installable
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).

Answer 1

OK, I found a solution. Maybe it will be helpful for somebody facing similar problems:

• This problem: You might want to run 'apt --fix-broken install' to correct these. The following packages have unmet dependencies: was caused by broken MidiEditor package, when I uninstalled it apt started to work properly
• Then I installed sudo apt-get install fluidsynth which installed qsynth also.
• I realized that qsynth complains that the JACK server is not working
• So I installed sudo apt install qjackctl
  • it asked me for permission, to give it real-time kernel rights. Not sure what that is, but I complied.
• Qtractor now does not complain, but I was still not getting any sound (MIDI seems to play but silently)
• So I was looking at the Qsynth Setup... button and found that the Soundfonts tab is empty. So I added some .sf2 file there using the Open... button
• I restarted Qtractor and now it pays the MIDI-file just fine