Apple DVD Studio Pro 4 - Manual (Page 223)

If you set a menu’s background asset to something that is non-standard, for example, a
still that is 800 x 600, the menu’s resolution changes to the highest resolution that is
smaller than the non-standard size (in this example, full D1, which is 720 x 480 for NTSC
or 720 x 576 for PAL), and the image is scaled to fit. If you set a menu’s background to
something that is smaller than full D1, it is scaled up to the full D1 size.
Note: As with SD-based DVD menus, when a menu’s background asset does not match
the 4:3 or 16:9 display mode, the empty areas are filled with the menu background color,
as defined in the Menu pane of DVD Studio Pro Preferences.
You must also be aware that the limit on the number of buttons your menu can have is
different than with SD-based DVD menus. Menus using the 4:3 aspect ratio can have up
to 48 buttons. Menus using the 16:9 Pan-Scan or 16:9 Letterbox modes can have up to
24 buttons. Menus using the 6:9 Pan-Scan & Letterbox modes can have up to 16 buttons.
Adding Intro and Transition Clips to Menus
You can make the DVD viewing experience more polished by adding short video clips
that play at the beginning of a menu (intro clips) and when buttons are pressed (transition
clips).
There are several approaches you can take to add these clips to your project. See Adding
Intro and Transition Clips to Menus for more information.
223 Chapter 12 Introduction to Creating Menus