When creating a new project, I have 2 HDV options on the General page; HDV 720 and HDV 1080i, but no choices for the File format on the Video Rendering page, I-frame only Mpeg 2 is greyed out. If you shot in the HDV mode, choose one of the HDV presets that matches your camera setting…720 or 1080i.
HDV is basically Mpeg2 I frame only on the DV tape which is then converted to an intermediate codec for editing.