You can find a PDF version of the Linux DVB API version 3 in the download area.
A browsable online version of the Linux DVB API version 3 documentation (generated with latex2html from TeX sources in the CVS) is here.
A small collection of READMEs and FAQs is included in the Linux kernel source tree in linux/Documentation/dvb/ ( browse docs in CVS).
You can find a PDF version of Video4Linux API (version 2) at download area.
A browsable online version of Video4Linux API (version 2) is at here.
There's a new V4L Drivers guide at here
PS.: This is a newer documment and might be suject to some errors. Contributions are wanted. Also notice that the main guide shall always be V4L API2.
Video4Linux API (version 1) is obsolete. It will be removed from kernel by July/2006.