Build python-opencv with gstreamer support

build_opencv_with_gstreamer.sh

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+#!/bin/bash
+# When using RTSP gstreamer can provides a way lower latency then ffmpeg
+# and exposes more options to tweak the connection. However, the pypi
+# version of python-opencv is build without gstreamer. Thus, we need to
+# build our own python wheel.
+
+# adapted from https://github.com/opencv/opencv-python/issues/530#issuecomment-1006343643
+
+# install gstreamer dependencies
+sudo apt-get install --quiet -y --no-install-recommends \
+  gstreamer1.0-gl \
+  gstreamer1.0-opencv \
+  gstreamer1.0-plugins-bad \
+  gstreamer1.0-plugins-good \
+  gstreamer1.0-plugins-ugly \
+  gstreamer1.0-tools \
+  libgstreamer-plugins-base1.0-dev \
+  libgstreamer1.0-0 \
+  libgstreamer1.0-dev 
+
+# ffmpeg deps
+sudo apt install ffmpeg libgtk2.0-dev libavformat-dev libavcodec-dev libavutil-dev libswscale-dev libtbb-dev libjpeg-dev libpng-dev libtiff-dev
+
+OPENCV_VER="84" #fix at 4.10.0.84, or use rolling release: "4.x"
+STARTDIR=$(pwd)
+TMPDIR=$(mktemp -d)
+
+# Build and install OpenCV from source.
+echo $TMPDIR
+
+# pyenv compatibility
+cp .python-version $TMPDIR
+
+cd "${TMPDIR}"
+git clone --branch ${OPENCV_VER} --depth 1 --recurse-submodules --shallow-submodules https://github.com/opencv/opencv-python.git opencv-python-${OPENCV_VER}
+cd opencv-python-${OPENCV_VER}
+export ENABLE_CONTRIB=0
+# export ENABLE_HEADLESS=1
+# We want GStreamer support enabled.
+export CMAKE_ARGS="-DWITH_GSTREAMER=ON -DWITH_FFMPEG=ON"
+python -m pip wheel . --verbose -w $STARTDIR
+
+# # Install OpenCV
+# python3 -m pip install opencv_python*.whl
+# cp opencv_python*.whl $STARTDIR