V4L2 API Specification (Revision 0.24)

V4L2 Mini-FAQ

Q: That's the V4L2 spec, what about V4L?
A: /usr/src/linux/Documentation/video4linux/API.html
and http://linuxtv.org/downloads/video4linux/API/V4L1_API.html

Q: Are there any examples?
A: Yes, in the spec. Also a complete video capture example, source is capture.c.

Q: I have more questions.
A: Try the V4L Wiki or the Video4Linux mailing list.