What is the default behaviour? Will extras install when not explicitly requested during pip install?

I am working on setup.py for package, which has optional dependency on OpenCV for webcam support, but it can work even without webcam.

Problem is that on ARM systems, there is no OpenCV package available in PyPI. So i would like my package to install without it. I've understood, that i can add it to extras_require={}, but i am not sure how this will work.

When people do pip install mypackage i want webcam support to install if available, but to be silently ignored if not available. But i am afraid that it will install only if people will do pip install mypackage[webcam].

What is the default behaviour? Will extras install when not explicitly requested during pip install?