TV broadcast has the following pecularity that the whole picture with frame rate 25 (24) Hz is split into two parts, so called fields. One field contain odd lines and another even lines. Then these fields are translated with frequency 50 fields per second. You see 50 fileds in one second on your TV set. Viewing of such translation on TV set is quite comfortable because two field are drawn subsequently one by one and even lines of one field will be shown in place between odd lines of other field. When you are viewing video on PC, it is drawn the whole frame, that obtained by combining two fields together. If you are viewing the material shoot on film, there is no problem, because this combining restores original frame from film. But video camera gets the ready signal from matrix in fields, not whole frames, with frequency 50 fields per second. Thus if there is motion in frame, the next field will capture the moment that differs by 1/50 of second in time. When you combine every two subsequent fields in progressive frame odd lines will be get from one field and even from another. Since there is the difference of 20 ms in time between them there will be a comb on the edges of moving objects.
Tu suppress this effect on video materials you need to add one of the deinterlace filters in "Video" settings – "Video processing setting for preview". Also you may use hardware deinterlace if your VGA card supports this function.