How to install openboard for 18.04?

I know that openboard is officaly only released for 16.04. Is there any chance to get it working under 18.04?

This is what I tried:

$ sudo gdebi openboard_ubuntu_16.04_1.5.2_amd64.deb 
  Reading package lists... Done
  Building dependency tree        
  Reading state information... Done
  Reading state information... Done
  This package is uninstallable
  Dependency is not satisfiable: libavformat-ffmpeg56 (>= 7:2.8.15)

This is my ffmpeg version that I have currently installed:

ffmpeg version n4.1 Copyright (c) 2000-2018 the FFmpeg developers

I managed to install it with with flathub: https://flathub.org/apps/details/ch.openboard.OpenBoard

I managed to install it from sources on Ubuntu 18.04 LTS (and Ubuntu 20.04 LTS too), following the instructions provided at the OpenBoard github site, "Building from source".

I report hereinafter the steps with some very minor modification:

Install the required dependencies

sudo apt-get install git qt5-default libqt5svg5-dev libqt5webkit5-dev libqt5xmlpatterns5-dev qtscript5-dev libssl-dev libpaper-dev libmotif-dev qtmultimedia5-dev qttools5-dev

Create a temporary build directory, and move there to download the required code

 git clone https://github.com/OpenBoard-Org/OpenBoard.git
 git clone https://github.com/OpenBoard-Org/OpenBoard-Importer.git
 git clone https://github.com/OpenBoard-Org/OpenBoard-ThirdParty.git

Build the Third-Party libraries

cd OpenBoard-ThirdParty/freetype
qmake freetype.pro -spec linux-g++
make

cd ../quazip
qmake quazip.pro -spec linux-g++
make

cd ../xpdf/xpdf-3.04
./configure --with-freetype2-library="../../freetype/lib/linux" --with-freetype2-includes="../../freetype/freetype-2.6.1/include"
cd ..
qmake xpdf.pro -spec linux-g++
make

Build the Open-Sankoré document importer (this is suggested as optional... in my case I tried it anyway)
```
cd ../OpenBoard-Importer
qmake OpenBoardImporter.pro -spec linux-g++
make
```

Build OpenBoard

cd ../OpenBoard
qmake OpenBoard.pro -spec linux-g++-64
make

If you follow the instructions there, the final make will fail by showing some missing dependencies. However, by looking for the names of the corresponding missing libraries in a package manager (for example, the Synaptic package manager), it is relatively easy to find the corresponding missing development packages (that is, the packages that end with -dev; in my case, these were libswscale-dev, libva-dev, libxcb-shm0-dev, libxcb-xfixes0-dev, libasound2-dev, libsdl2-dev, libsdl1.2-dev, libx264-dev, libvpx-dev, libvorbis-dev, libtheora-dev, libopus-dev, libmp3lame-dev, libfdk-aac-dev, libass-dev, liblzma-dev, and libbz2-dev).