HW-Accelerated decoding USB wecam with OpenCV

I’ve been trying to get HW-accelerated decoding to work on my Jetson with OpenCV, without much success.
I can get it to work with gst-launch, but not in OpenCV.
I’m using a C920 webcam as an input, with MPEG gst-launch-1.0 v4l2src device="/dev/video0" io-mode=2 ! "image/jpeg, width=1920, height=1080, framerate=30/1" ! nvjpegdec ! "video/x-raw" ! nvoverlaysink -e and it works well, but as I understand it, I can’t use nvjpegdec in OpenCV because it overwrites jpegdec. So how can I compile OpenCV to be able to use it ?
I’ve also tried with H264, but framerate is very inconsistent, even in gst-launch.
I’ve also read that nvjpegdec isn’t supported for use in OpenCV, if so, how can I capture a cv::Mat from GStreamer in some way ?

Please try this command:
Set camera decoder in OpenCV on Jetson Nano - #8 by DaneLLL
You can use nvv4l2decoder to decoding JPEGs.

This works indeed (and around the same time I found a similar solution here : Save video with OpenCV and usb-webcamera ) but now i can’t sync my multiple cameras with OpenCV’s Grab function (they seem to be out a couple of frames). Can I do something similar with GStreamer, or as a workaround, use gstreamer to concatenate the cameras into one single image that’s time-synced in GStreamer ?

Could you go to OpenCV forum to get suggestion for the use-case? We don’t actually have experience about Grab functions. Users in the forum shall have more expertise in OpenCV functions.