you can check with getBuildInformation(), see “Video I/O” section. I’d assume that maybe the desktop java package comes with ffmpeg but certainly not the android one. it should only have system APIs enabled in its build.
I don’t have answers to your questions. maybe there are answers. I don’t know them. my not knowing should not be construed as those answers not existing. I am not one who is supposed to know this stuff.
you could browse the issues on OpenCV’s github for any information. that is assuming (I didn’t look) that there’s nothing in the actual documentation.
some third party libraries are included by source in OpenCV’s repo. those probably have a certain kind of license that is sufficiently permissible.
if what you’re looking for doesn’t exist yet, you could try to convince the OpenCV developers to prepare such a legalese document for each release.
personally, I’d deal with lawyers by planting them in the back yard. you might wanna retain one of them to make sure similar approaches are all above board.