@Honey_Patouceul
Thank you for your hint. Unfortunately, -D WITH_FFMPEG=ON alone does not the trick. If you end up with an OpenCV build including FFMPEG support depends on, if CMake was able to compile a little FFMPEG test build. There can be many reasons why this can fail (e.g. static libraries).
Nevertheless, your link was very helpful because it (together with many other hints here and there) helped me to figure out some additional prerequisites in order to get a successful OpenCV build including CUDA and FFMPEG.
For those who want to try their luck as well, I put together all my learnings here. Starting from a fresh Jetpack 4.5.1, you should be able to get OpenCV 4.5.3 with CUDA acceleration and FFMPEG 4.2.4 including the hardware acceleration patch from jocover. You find my description here: Hardware accelerated OpenCV 4.5.3 build with FFMPEG 4.2.4 on NVidia Jetson · GitHub
@DaneLLL
I understand that you want to push Jetson users into NVidia frameworks like VPI, but unfortunately, this has no Python binding. As I wrote before, I need a solution based on OpenCV and FFMPEG with good portability to other platforms and - if running on Jetson - utilizing it’s hardware acceleration.
Now, with the description given in my gist, I was successful.