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Argus Encoder Family Version 2.6 API Developer’s Guide
GOP Structure and Size
GOP Structure and Size
A GOP (group of pictures) is composed of a combination of I frames, B frames,
and P frames. The only required frame type in a GOP is the I frame. If P and B
frames are included in a GOP, they are arranged in repeated fixed sequences.
The Argus encoder allows from 1 to 16 frames per GOP. A GOP can be closed (it
can be decoded by itself, with no reference to a previous or subsequent GOP) or
open (it cannot stand alone). If the GOP is an open GOP, it composed of an intro-
ductory “I” frame, followed by one of the following:
• From 0 to 15 “P” frames.
• From 0 to 7 “BP” groups, followed by a single “B” at the end.
• From 0 to 4 “BBP” groups, followed by a “BB” pair at the end.
If the GOP is a closed GOP, it is composed of an introductory “IP” frame combi-
nation, followed by one of the following:
• From 0 to 14 “P” frames.
• From 0 to 6 “BP” groups, followed by a single “B” at the end.
• From 0 to 4 “BBP” groups, followed by a “BB” pair at the end.
For all acceptable GOP structures, the I-frame distance (or “N” value in MPEG
terminology) is defined as the number of frames between I frames, including the
first, but excluding the second. The reference frame distance (or “M” value in
MPEG terminology) is defined as the number of frames between reference frames
(where “I” and “P” are reference frames), including the first, but not including the
second. Note that the introductory closed-GOP “P” frame is
not
considered when
calculating the reference frame distance.
4:2:0
1 (MPEG-2)
704
576
4:2:0
1 (MPEG-2) (Half-D1)
352
576
4:2:0
0 (MPEG-1 SIF)
352
288
Format
Chroma
Mode
Horizontal
Res
Vertical
Res
Table A-2. Allowable Combinations of Video Properties (Continued)