question about GOP

Giganews Newsgroups
Subject: question about GOP
Posted by:  joggingso…@gmail.com
Date: Tue, 6 May 2008

Hi, all
  I read the following words from the internet:

When you encode to MPEG2 you have to set the GOP structure, this is
how many P and B frames    (called delta frames) follow an I frame
( a keyframe), but with MPEG4 there is no need to use such a fixed and
pre-determined GOP, instead you can tell the MPEG4 codec at what
interval you wish to use a Keyframe, or instead of that you can tell
it to use a keyframe upon a certain % level of scene change.

I don=92t understand why. Can anyone clarify it for me?  Why GOP level
is needed?
Also a GOP header is optional. Few information is contained in a GOP
header.

Best Regards
Jogging

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