ok, since nobody replied i kept searching the answer.
here it is :
in HDV, the video frame is defined to have an aspect ratio of 16:9. Permitted resolutions are 720p and 1080i.
HDV 720p uses a resolution of 1280x720 square pixels. HDV 1080i uses a resolution of 1440×1080 pixels, but is still displayed with a device aspect ratio of 16:9 This is because the pixel aspect ratio is 1.33:1 stretching the actual pixels to make the proper resolution. This means it has lower horizontal resolution than true 1080 HD formats (1920x1080), but the same applies also to most other widely used HD formats including XDCAM HD, DVCPRO HD and HDCAM, all of which have the same or lower resolution as HDV.
more here : HDV - Wikipedia, the free encyclopedia