It's not possible to use media-libs/smpeg for developing on Gentoo. #include <smpeg/smpeg.h> results in: /usr/include/smpeg/smpeg.h:25:17: error: SDL.h: No such file or directory /usr/include/smpeg/smpeg.h:26:23: error: SDL_mutex.h: No such file or directory /usr/include/smpeg/smpeg.h:27:23: error: SDL_audio.h: No such file or directory .
You should be using /usr/bin/smpeg-config --cflags to set the proper flags to pass to your C compiler.