The following is from the DVDit web site
(http://sonic.com/).

So, can the GOP be adjusted by VF?

Chuck Rosengard


Number of Pictures in a GOP
A GOP (group of pictures) is a unit of MPEG that begins
with an I-frame
(essentially, a keyframe) and ends with a P-frame (an MPEG
difference
frame that refers to previous frames). Changing the size of
the GOP affects
the number of I-frames, which in turn affects the data rate.
The standard MPEG GOP is 15 frames, and this is the
preferred value for
MPEG-2 files used in DVDit! The size of the GOP must be the
same for all
video files in a DVDit! Project.
Your MPEG encoding application may also allow you to
specify a
reference interval, which determines the distance between P-
frames in a
GOP. The normal value for this parameter is 3. If you
decide to change it, be
sure that you choose a number that is evenly divisible into
the GOP size
(for example, if the GOP is 15 frames, acceptable values
are 1, 3 and 5).

Charles Rosengard wrote:
>>The same error is reported by Sonic (different company)
>>DVDit. I also noted that the DVD mpeg2 audio standard is
>>48K Hz, not the 44K Hz that VF defaults to. That is easy
>>enough to change. I will watch this threat for
information
>>on headers and sequence, however.
>>
>>Chuck
>>
>>Randy Olson wrote:
>>>>I am using Video Factory inconjunction with a capture
>>>>system called Dazzle. It comes with a package to creat
>>DVDs
>>>>called MyDVD.
>>>>
>>>>I created the videos with Video Factory. MyDVD
says "Each
>>>>GOP header must be preceeded by a sequence header." How
>>do
>>>>I tell Video Factory to include a sequence header?