Did you build OpenCV from source?
Live Streaming over USB on Ubuntu and Linux, NVIDIA Jetson - #78 by zdydek
gscam doesn’t seem to handle udp streams well. I also tried using OpenCV VideoCapture to get the data into ros, but that had a couple issues. There are two APIs for VideoCapture that seemed appropriate: Gstreamer and FFmpeg. It turns out that the OpenCV version packaged with ROS is not built with Gstreamer support, so you would have to build OpenCV yourself to use it. For FFmpeg, the version of OpenCV packaged with ROS melodic is 3.2, which is missing a fairly critical change here: https://github.com/opencv/opencv/pull/9292 that allows you to set FFmpeg capture options in an environment variable. I got both of these working by upgrading OpenCV to version 3.4.9 and building from source, but Gstreamer had a low framerate (~5fps) and FFmpeg had a lot of corruption and dropped frames (maybe it was stuck using UDP?). So, I decided to stick with gscam for now.
The latency value of 400 worked for me, but should be tuned depending on your network.