User guide

224
Chapter 9, Using Matrox MediaExport
$ Subgroup Length Determines the subgroup length of B-frames and/or
P-frames in the GOP, after the initial I-frame. A subgroup of 3 appears as
“BBP,” a subgroup of 2 appears as “BP,” and a subgroup of 1 gives you only
P-frames after the initial I-frame.
3 From the Put sequence header(s) list, select the placement frequency of
the sequence header. The sequence header of an MPEG file provides
information about the video stream for the decoder, such as bit rate, frame
rate, and aspect ratio. Some MPEG applications require a particular
frequency for the placement of the sequence headers in the file. For example,
DVD-compliant video requires a sequence header before every GOP in the
video file.
4 Under Maximum Motion Vectors, either select a preset value from the
lists, or enter a value for the size of your P frame and B frame motion
vectors. The quality of your images can be affected if the motion vector
values you choose are either too long, or too short. The best image quality is
most often achieved using vector lengths between 16 and 32.
¦NoteMotion vector values must be multiples of 8 between 16 and 64. If
needed, the value you enter will be set to the nearest supported value.