Standard definition video uses a 4:3 aspect ratio. No matter what the size of the display,
the height is always 75 percent of the width. This is true for both NTSC, which has 525
lines in each frame (480 of these active with DVDs), and PAL, which has 625 lines per
frame (576 active). Both standards also have 720 pixels per line when converted to MPEG.
To fit the 4:3 aspect ratio perfectly using square pixels and 720 pixels per line, there would
have to be 540 lines in each frame. So for NTSC, which has 480 lines, the lines must be
spaced slightly apart to fill the same area, resulting in rectangular pixels. For PAL, with
576 lines, they must be squeezed together slightly to fit.
The Settings pop-up menu in the DVD Studio Pro Menu Editor has a square/rectangular
pixel selection that allows you to choose whether to view menu graphics as rectangular
pixels (forcing a 4:3 aspect ratio) or as square pixels while creating menus. The Viewer
tab also has the same settings. The Simulator always shows rectangular pixels, simulating
what the viewer will see.
The real problem arises when you create your menu graphics.