1. hybrid-vapoursynth-addon Adding Vapoursynth and plugins to Hybrid
2. extract the folder to a temporary folder
3. make the build-vapoursynth.sh script executable chmod +x build-vapoursynth.sh and run it.
4. When it's finished add:

   export LD_LIBRARY_PATH=~/opt/vapoursynth/lib
   export PYTHONPATH=~/opt/vapoursynth/lib/python3.6/site-packages
   export PATH="~/opt/vapoursynth/bin:$PATH"
   export PATH="~/.local/bin:$PATH"
   

to your ~/.profile- and ~/.bashrc -file, close the terminal and open a new terminal, best use absolute paths.

Side notes:

• depending on your Python version you need to adjust pyhton3.6 accordingly and if you changed the default paths inside the config.txt youe need to adjust them here too.
• in Ubuntu 20.04 I had to use absolute paths so instead of ~/... I had to use /home/selur/...

5. Calling vspipe --version should output something like:

   VapourSynth Video Processing Library
   Copyright (c) 2012-2020 Fredrik Mellbin
   Core R49
   API R3.6
   Options: -
   

6. reboot your system. (vspipe --version should now work without having to enter the export calls)
7. make the build-plugins.sh executable chmod +x build-plugins.sh and run it (this will take quite a while).

Now Hybrid will be able to use Vapoursynth.

Note: building RIFE (https://github.com/HomeOfVapourSynthEvolution/VapourSynth-RIFE-ncnn-Vulkan) requires VULKAN SDK installed on Ubuntu 18.04:

wget -qO - http://packages.lunarg.com/lunarg-signing-key-pub.asc | sudo apt-key add -
sudo wget -qO /etc/apt/sources.list.d/lunarg-vulkan-bionic.list http://packages.lunarg.com/vulkan/lunarg-vulkan-bionic.list
sudo apt update
sudo apt install vulkan-sdk

on Ubuntu 20.04:

wget -qO - http://packages.lunarg.com/lunarg-signing-key-pub.asc | sudo apt-key add -
sudo wget -qO /etc/apt/sources.list.d/lunarg-vulkan-focal.list http://packages.lunarg.com/vulkan/lunarg-vulkan-focal.list
sudo apt update
sudo apt install vulkan-sdk

on Ubuntu 22.04:

wget -qO- https://packages.lunarg.com/lunarg-signing-key-pub.asc | sudo tee /etc/apt/trusted.gpg.d/lunarg.asc
sudo wget -qO /etc/apt/sources.list.d/lunarg-vulkan-jammy.list http://packages.lunarg.com/vulkan/lunarg-vulkan-jammy.list
sudo apt update
sudo apt install vulkan-sdk