Apple Compressor 3 - Manual (Page 206)

• Open and Closed buttons: Closed GOPs do not contain any frame that refers to a frame
in the previous or next GOP, while open GOPs begin with one or more B-frames that
reference the last P-frame of the previous GOP. Closed GOPs created by the Compressor
MPEG-2 encoder begin with an I-frame. Choose your GOP type (open or closed) based
on 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
Open and Closed
GOPs for more information.
• Open: Select this button to create open GOPs.
• Closed: Select this button to create closed GOPs.
• GOP Size pop-up menu: Choose how many frames are contained within your GOP,
following the format of the chosen GOP structure. The maximum GOP size you can
choose within Compressor is 15 frames (NTSC) or 12 frames (PAL and 720p). The
minimum GOP size for all video formats is 6 frames (closed GOP) or 7 frames (open
GOP). The relationship between GOP structure and GOP size gives you GOP patterns.
See
Understanding GOPs and Frame Types and GOP Size for more information.
• Pattern field: This field cannot be edited but displays the actual GOP pattern based on
your chosen GOP structure and size.
206 Chapter 18 Creating MPEG-2 Output Files