diff --git a/dev-docs/build.md b/dev-docs/build.md
index 949382dd0..e974b99f5 100644
--- a/dev-docs/build.md
+++ b/dev-docs/build.md
@@ -1,157 +1,160 @@
 # Building Kdenlive
 
 ## Base procedure
 
 Kdenlive usually requires the latest version of MLT, in which go several API updates, bufixes and optimizations.
 
 ### Get the build dependencies
 
 You can use your distribution packages information (if not too old) to easily get a complete build environment:
 
 ```bash
 # Debian/Ubuntu -- Enable deb-src entries /etc/apt/sources beforehand
 sudo apt build-dep mlt kdenlive
 # Fedora/CentOS -- Install builddep beforehand
 dnf builddep mlt kdenlive
 # OpenSUSE
 zypper source-install --build-deps-only mlt kdenlive
 ```
 
 ### Clone the repositories
 
 In your development directory, run:
 
 ```bash
 git clone https://github.com/mltframework/mlt.git
 git clone https://invent.kde.org/multimedia/kdenlive.git
 ```
 
 ### Build and install the projects
 
 You should decide where you want to install your builds:
 
 - by default it goes to `/usr/local` (good option if you are admin of the machine, normally programs there are automatically detected);
 - you may use `$HOME/.local` user-writable directory (good option if you don't want to play with admin rights, programs there are also usually found)
 - you may want to override the distribution files in `/usr` (then you have to remove MLT & Kdenlive binary & data packages first)
 - you can pick any destination you like (eg in `/opt` or anywhere in `$HOME`, then you will have to set several environment variables for programs, libs and data to be found)
 
 Let's define that destination as `INSTALL_PREFIX` variable; also you can set `JOBS` variable to the number of threads your CPU can offer for builds.
 
 And build the dependencies (MLT) before the project (Kdenlive):
 
 ```bash
 INSTALL_PREFIX=$HOME/.local # or any other choice
 JOBS=4
 
 # MLT
 cd mlt
-./configure --enable-gpl --enable-gpl3 --prefix=/home/soft/kdenlive
+./configure --enable-gpl --enable-gpl3 --prefix=$INSTALL_PREFIX
 make -j$JOBS
 make install
 # 'sudo make install' if INSTALL_PREFIX is not user-writable
 
 # Kdenlive
 cd ../kdenlive
 mkdir build
 cd build
 cmake .. -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX
 make -j$JOBS
 make install
 # 'sudo make install' if INSTALL_PREFIX is not user-writable
 ```
 
 Note that `make install` is required for Kdenlive, otherwise the effects will not be installed and cannot be used.
 
 ### Run Kdenlive
 
 If you didn't build in a system path in which all libs and data are automatically found, you will need to set environment variables to point to them.
 This is done by the auto-generated script in `kdenlive/build` that must be sourced (to keep variables set in current shell, unlike just executing the script):
 
 ```bash
 . prefix.sh
 kdenlive
 ```
 
 ## Various development tricks
 
 ### Debugging
 
 Having debug symbols helps getting much more useful information from crash logs or analyzers outputs; this is enabled at configure stage.
 - in MLT, append `--enable-debug` to `./configure` line
 - in Kdenlive, append `-DCMAKE_BUILD_TYPE=Debug` to `cmake` line
 
 ### Running tests
 
 Kdenlive test coverage is focused mostly on timeline model code (extending tests to more parts is highly desired). To run those tests, append to `cmake` line:
 `-DBUILD_TESTING=ON`
 
 ### Fuzzer
 
 Kdenlive embeds a fuzzing engine that can detect crashes and auto-generate tests. This can be activated in `cmake` line with:
 `-DBUILD_FUZZING=ON`
 
 ### Speeding up compilations
 
 Ninja build systems, compared to make, seems faster and better detecting which files are necessary to rebuild. You can enable it appending `-GNinja` to `cmake` line
 CCache also helps: `-DCMAKE_CXX_COMPILER_LAUNCHER=ccache`
 
 ### Analyzers
 
 You can configure Kdenlive to embed tooling for runtime analysis, for example appending to cmake line:
 `-DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DECM_ENABLE_SANITIZERS='address'`
 
 This one will report in terminal all memory handling errors found during execution.
 
 ### Building OpenCV tracking module
 
 MLT/Kdenlive tracking effect relies on a "contrib" a OpenCV module that is not shipped by distributions.
 We build it in our AppImage but you may want it on your system (note OpenCV deserves its reputation of being difficult to build!).
 
 ```bash
 wget https://github.com/opencv/opencv/archive/4.3.0.tar.gz -O opencv-4.3.0.tar.gz
 wget https://github.com/opencv/opencv_contrib/archive/4.3.0.tar.gz -O opencv_contrib-4.3.0.tar.gz
 tar xaf opencv-4.3.0.tar.gz
 tar xaf opencv_contrib-4.3.0.tar.gz
 cd opencv-4.3.0
 mkdir build
 cd build
 cmake .. -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX \
+  -DOPENCV_EXTRA_MODULES_PATH=../../opencv_contrib-4.3.0/modules \
   -DOPENCV_GENERATE_PKGCONFIG=ON -DBUILD_LIST=tracking -DOPENCV_BUILD_3RDPARTY_LIBS=OFF
 ```
 
+Then you will have to rebuild MLT appending `--enable-opencv` to `configure` line!
+
 ### Building frei0r
 
 You may be interested in building latest frei0r effects library. So get dependencies, clone repository, and build-install:
 
 ```bash
 sudo apt build-dep frei0r
 git clone https://github.com/dyne/frei0r.git
 cd frei0r
 mkdir build
 cd build
 cmake .. -DWITHOUT_OPENCV=true -DCMAKE_INSTALL_PREFIX=$INSTALL_PREFIX
 ```
 
 Note: as of 20.04, frei0r doesn't support recent OpenCV (and effects using it seemed not very stable)
 
 ### Building in Docker
 
 It is possible to run the above commands inside a container, with a fresh Ubuntu for example.
 Note that Kdenlive cannot be easily run from inside the Docker container as it is a GUI application.
 
 ```bash
 # Spin up a Docker container
 # The --rm flag removes the container after it is stopped.
 docker run -it --rm ubuntu:20.04
 
 # Now install the dependencies etc.
 # Note that you are root in the container, and sudo neither exists nor works.
 apt install …
 
 # When you are done, exit
 exit
 ```
 
 ## Translating Kdenlive
 
 TODO