Okay, I was able to compile it using this script, its essentially the same as the post, but with the addition of the gstreamer
#instructions:
apt upgrade && sudo apt upgrade
sudo dpkg --add-architecture armhf
sudo apt update
sudo apt install qemu-user-static
apt-get install python3-dev
apt-get install python3-numpy
apt-get install python-dev
apt-get install python-numpy
apt-get install libpython2-dev:armhf
apt-get install libpython3-dev:armhf
apt install libtiff-dev:armhf zlib1g-dev:armhf
apt install libjpeg-dev:armhf libpng-dev:armhf
apt install libavcodec-dev:armhf libavformat-dev:armhf libswscale-dev:armhf libv4l-dev:armhf
apt install libxvidcore-dev:armhf libx264-dev:armhf
apt install crossbuild-essential-armhf
apt install gfortran-arm-linux-gnueabihf
sudo apt install cmake git pkg-config wget
cd ~
mkdir opencv_all && cd opencv_all
wget -O opencv.tar.gz https://github.com/opencv/opencv/archive/4.1.0.tar.gz
tar xf opencv.tar.gz
wget -O opencv_contrib.tar.gz https://github.com/opencv/opencv_contrib/archive/4.1.0.tar.gz
tar xf opencv_contrib.tar.gz
rm *.tar.gz
export PKG_CONFIG_PATH=/usr/lib/arm-linux-gnueabihf/pkgconfig:/usr/share/pkgconfig
export PKG_CONFIG_LIBDIR=/usr/lib/arm-linux-gnueabihf/pkgconfig:/usr/share/pkgconfig
apt install gstreamer1.0-tools:armhf libgstreamer1.0-dev:armhf libgstreamer-plugins-base1.0-dev:armhf
cd opencv-4.1.0
mkdir build && cd build
cmake -D CMAKE_BUILD_TYPE=RELEASE \
-D CMAKE_INSTALL_PREFIX=/opt/opencv-4.1.0 \
-D CMAKE_TOOLCHAIN_FILE=../platforms/linux/arm-gnueabi.toolchain.cmake \
-D OPENCV_EXTRA_MODULES_PATH=~/opencv_all/opencv_contrib-4.1.0/modules \
-D OPENCV_ENABLE_NONFREE=ON \
-D ENABLE_NEON=ON \
-D ENABLE_VFPV3=ON \
-D BUILD_TESTS=OFF \
-D BUILD_DOCS=OFF \
-D PYTHON2_INCLUDE_PATH=/usr/include/python2.7 \
-D PYTHON2_LIBRARIES=/usr/lib/arm-linux-gnueabihf/libpython2.7.so \
-D PYTHON2_NUMPY_INCLUDE_DIRS=/usr/lib/python2/dist-packages/numpy/core/include \
-D PYTHON3_INCLUDE_PATH=/usr/include/python3.7m \
-D PYTHON3_LIBRARIES=/usr/lib/arm-linux-gnueabihf/libpython3.7m.so \
-D PYTHON3_NUMPY_INCLUDE_DIRS=/usr/lib/python3/dist-packages/numpy/core/include \
-D BUILD_OPENCV_PYTHON2=ON \
-D BUILD_OPENCV_PYTHON3=ON \
-D WITH_GSTREAMER=ON \
-D BUILD_EXAMPLES=OFF ..