Under CCE could someone tell me what the GOP Settings and the timecode setting is ??

Also on one of the doom9 guides for encoding a dvd > dvdr with cce it says to first do one pass vbr with a quantization and bitrate,then run it through again and do a multipass vbr.I dont understand the point in doing this as it would take alot longer,y not just do a multipass vbr?