Apple Compressor 3 - Manual (Page 205)

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 pop-up menu: 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. Choose from one of the
following:
Note: For most MPEG-2 encoding situations intended for use on a DVD, choose IBBP
as the GOP structure setting, and GOP size 15 for NTSC, or GOP size 12 for PAL. These
selections will give the best results in most situations. See
GOP Structure for more
information.
• IP: No B-frames are used with this setting. Choose IP only if your media contains fast
motion that does not encode with sufficient quality using an IBBP or IBP structure.
• IBP: One B-frame is used between reference frames (I-frames and P-frames) with IBP.
Choose this setting only if your media contains fast motion that does not encode
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.
205 Chapter 18 Creating MPEG-2 Output Files