This replaces the original mjpeg_encoder API with a VideoEncoder base
class which can be reimplemented by other encoders.
This also renames the members and enums from mjpeg_* to video_*.
Signed-off-by: Francois Gouget <fgouget@codeweavers.com>
Acked-by: Christophe Fergeau <cfergeau@redhat.com>