Apple Compressor 3 - Manual (Page 220)

Note: Your choice of GOP type (Open or Closed) may be influenced by whether and
how you create chapter markers for DVD authoring with DVD Studio Pro and whether
you intend to use multiple video angles in your title. See
More About GOPs and Markers
and Adding Chapter or Podcast Markers to a Clip for more information.
220 Chapter 18 Creating MPEG-2 Output Files