(4) Subsections (1), (2) and (3) also apply, with such modifications as are necessary, in relation to a film which was, or is alleged to have been, jointly directed as they apply to a work which is, or is alleged to be, a work of joint authorship; and for the purpose of this subsection, a film is “jointly directed” if it is made by the collaboration of two or more directors and the contribution of each director is not distinct from that of the other director or directors.