This is an exclusive Japanese connector for analog video formats using component only, YPbPr. All D formats are compatible with their lower number cousins, IE a D3 also handles D2 and D1 formats or a D5 handles all formats.
D1 video - 525I / 480I
D2 video - 525P / 480P
D3 video - 1125I / 1080I / 1035I
D4 video - 750P / 720P
D5 video - 1125P / 1080P (future use)
More info
http://en.wikipedia.org/wiki/D4_video_connector