Apple Compressor (4.0) - Manual (Page 95)

Chapter 5 Custom settings and output formats 95
GOP tab
You use the GOP (group of pictures) tab to select a GOP format, structure, and size. For more
information, see
About GOPs (groups of pictures) on page 99.
Note: If you choose any of the HD video formats in the Video Format tab, the settings in the GOP
tab cannot be changed and default to a closed IBBP GOP structure with a size of 12 (for PAL) or
15 (for NTSC).
•
GOP Structure: Choose an option from this pop-up menu to specify whether there will be two,
one, or no B-frames between the reference frames within a GOP. GOP structure, along with
GOP size, determines the number of I-frames, P-frames, and B-frames that are used within a
GOP during encoding.
Note: For most MPEG-2 encoding situations intended for use on a DVD, choose IBBP as the GOP
structure setting, and a GOP size of 15 for NTSC, or 12 for PAL. These selections give the best
results in most situations. For more information, see
About GOPs (groups of pictures) on page 99.
•
IP: No B-frames are used with this setting. Choose IP only if your media contains fast motion
that isn’t encoded with sufficient quality using an IBBP or IBP structure.
•
IBP: One B-frame is used between reference frames (I-frames and P-frames). Choose this
setting only if your media contains fast motion that isn’t encoded with sufficient quality
using an IBBP structure.
•
IBBP: Use IBBP for the majority of MPEG-2 encoding situations, along with a GOP size of 15
for NTSC, or 12 for PAL. Two B-frames are used between reference frames with this setting.
•
Open and Closed: Closed GOPs don’t contain any frame that refers to a frame in the previous
or next GOP, whereas 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. Select your GOP type (open or closed) based on whether and how you create
chapter markers for DVD authoring and whether you intend to use multiple video angles in
your title. For more information, see
About GOPs (groups of pictures) on page 99.
•
Open: Select this option to create open GOPs.
•
Closed: Select this option to create closed GOPs.