Apple DVD Studio Pro 4 - Manual (Page 120)

About NTSC and PAL Alpha Transitions
Each Alpha Transition is either NTSC or PAL. DVD Studio Pro uses the frame rate of the
transition assets to determine whether they are NTSC or PAL. Only those appropriate to
the current project’s video standard are available in DVD Studio Pro.
Note: Alpha Transitions using a frame rate of 24 fps can be used only in NTSC projects,
though they may show undesirable artifacts when the frame rate is scaled to match the
project.
120 Chapter 8 Preparing Alpha Transitions