Compressor 4 - GOP Tab

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.

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• 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. 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. 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.

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