Trying to get OpenCV (built with CUDA) working with FFMPEG

For hardware acceleration in ffmpeg, please refer to Jetson Nano FAQ
[Q: Is hardware acceleration enabled in ffmpeg?]

The OpenCV package installed through SDKManager does not enable CUDA filter. Please run the script to manually enable it and re-build OpenCV:
JEP/ at master · AastaNV/JEP · GitHub

By default we support hardware acceleration in jetson_multimedia_api and gstreamer. If you require OPenCV CUDA filter in your use-case, we suggest run gstreamer + OpenCV or jetson_multimedia_api + OpenCV to get optimal performance. Please refer to the samples:
Nano not using GPU with gstreamer/python. Slow FPS, dropped frames - #8 by DaneLLL
LibArgus EGLStream to nvivafilter - #14 by DaneLLL