https://bugs.kde.org/show_bug.cgi?id=392245#c6 it's possible that missing build dependencies can pass the 'cmake' step, and only fail later due to missing libraries. In this specific case for me, it was missing gstreamer-video-1.0
I cannot reproduce, I get the following error message: CMake Error: The following variables are used in this project, but they are set to NOTFOUND. Please set them or make sure they are set and tested correctly in the CMake files: GSTREAMER_VIDEO_LIBRARY linked by target "gstkamosoqt5videosink" in directory /home/apol/devel/frameworks/kamoso/src/elements/gstqtvideosink linked by target "qtvideosink_autotest" in directory /home/apol/devel/frameworks/kamoso/src/elements/gstqtvideosink -- Configuring incomplete, errors occurred! See also "/home/apol/build-devel/frameworks/kamoso/CMakeFiles/CMakeOutput.log".
Oh you're right, it did fail. My bad, I guess my minor criticism was that it maybe wasn't clear enough what was missing (ie, missing gstreamer-video-1.0) that said, that's probably a minor issue, and not worth a formal bug, my bad.