I have a small ros node which uses opencv to read an image. There is no explicit mention of gstreamer in any header file, and yet the code fails like this:

rosrun esp32cam_to_ros esp32cam_to_ros_node 
OK[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (1743) handleMessage OpenCV | GStreamer warning: your GStreamer installation is missing a required plugin
[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (1758) handleMessage OpenCV | GStreamer warning: Embedded video playback halted; module uridecodebin0 reported: Your GStreamer installation is missing a plug-in.
[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (888) open OpenCV | GStreamer warning: unable to start pipeline
[ WARN:0] global ../modules/videoio/src/cap_gstreamer.cpp (480) isPipelinePlaying OpenCV | GStreamer warning: GStreamer: pipeline have not been created

I am quite confused. I thought that the opencv from libopencv-dev did not use gstreamer (I thought there were instructions for compiling from source to include gstreamer functionality, but I am trying to use the binary package, libopencv-dev). I could be wrong about this, so I welcome any clarification.

If the program really should be trying to use gstreamer for something, how can I work out which plug-in is missing ?