OPENEMBEDDED DEPENDS

Hi, I'm going to develop a project for BB using OE. I've already build
the environment required by the OE, and I've successfully create a
simple helloworld package.

Now I've to do the same thing using my own source code, in which I
need to include some header files such as SDL.h of the SDL library
and avcodec.h. My source code seems like this:

#include <SDL.h>
#include <avcodec.h>

I read OE's manual but I don't understand how can I correctly
configure the DEPENDS in my .bb configuration file in order to use
this header file in my project.

Is it enough to edit DEPENDS in this way:

DEPENDS = "libsdl ffmpeg" ?

Or I have to use the do_stage?

Thanks to every one.