Gop pattern, Gop length – Apple DVD Studio Pro 4 User Manual
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There are three aspects to choosing a GOP setting: the GOP pattern, the GOP length, and
whether the GOP is “open” or “closed.”
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Closed GOP
(IBBP, 15 Frames)
P
B
B
P
B
P
B
P
B
P
I
B
B
B
B
GOP Pattern
The GOP pattern determines the ratio of P- to B-frames within a GOP. The most common
patterns used for DVD are IBP and IBBP. All three frame types do not have to be used in
a pattern; an IP pattern is also used in special circumstances.
IBP and IBBP GOP patterns, in conjunction with longer GOP lengths, produce the most
efficient encodes. Smaller GOP patterns with shorter GOP lengths work better with video
that has quick movements.
Some encoders can force I-frames to be added sporadically throughout a stream’s GOPs.
These I-frames can be placed manually by someone watching for sudden video changes
or automatically by an encoder detecting scene changes. You can place markers in
Final Cut Pro to identify specific frames to have an I-frame, either for use as a chapter
marker or to manually identify high motion areas. See
for
more information.
The integrated MPEG encoder uses a GOP pattern of IBBP.
GOP Length
Longer GOP lengths produce more efficient encodes by reducing the number of I-frames
but are less desirable during short-duration effects such as quick fades and quick camera
pans.
• SD-Based DVDs: The maximum GOP length for SD projects is 18 frames for NTSC or
15 frames for PAL. The minimum GOP length depends on the GOP pattern. For example,
an IP pattern can have a length as short as two frames.
The integrated MPEG encoder uses a GOP length of 15 frames for NTSC and 12 frames
for PAL SD assets.
• HD-Based DVDs: Because HD projects can use both interlaced and progressive video
assets, they have different GOP length maximums.
• NTSC interlaced assets: 18 frames per GOP
• NTSC progressive assets: 36 frames per GOP
• PAL interlaced assets: 15 frames per GOP
• PAL progressive assets: 30 frames per GOP
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Chapter 4
Preparing Video Assets