Complex sentence: DVD-R do not have to be formatted before being recorded by a compatible DVD video recorder, because the two variants of the discs are written in different formats (see DVD + VR and DVD-VR respectively).
Split into simpler sentences: DVD-R do not have to be formatted before being recorded by a compatible DVD video recorder. This is because the two variants of the discs are written in different formats (See DVD + VR and DVD-VR respectively).