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
Adding Markers to Your Video
The integrated MPEG encoder uses a GOP pattern of IBBP.