Wrote video module export header (export.hpp)
Sketched VideoFile class
CMake compiles now the video module
Sketched VideoBuffer class
Sketched VideoStream class
Sketched Movie class
The main header includes the video module
CMake adds FFMPEG dependencies
VideoFile opens multimedia files
VideoFile is able to decode frames (with its read method)
Fixed CMake compilation

FFMPEG headers declared as extern C and fixed FFMPEG depedencies.
Added video example
Implemented Video::loadFromFile function
Implemented Video::getFrames function
SFML includes the video module headers
Sketched VideoSource class
Let avformat_open_input and avformat_close_input (de)allocate the format context

Thanks to Michael Bradshaw for his advices.
Forgot to deallocate the codec context

Thanks to Michael Bradshaw for pointing that out.
Forgot to free AVPacket after each call to av_read_frame

Thanks to Michael Bradshaw for pointed that out.
Fixed strange segmentation fault by printing something