Practical getting started: http://stackoverflow.com/a/40561598/895245
https://en.wikipedia.org/wiki/Video4Linux
Docs: https://linuxtv.org/docs.php Generated from their rst docs inside the Linux kernel tree.
Git: https://git.linuxtv.org/v4l-utils.git/
Examples in source tree: contrib/test
Can be used in Android apparently: http://stackoverflow.com/questions/2940001/android-v4l-or-v4l2