VCS VideoJet 8000, User Manual

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Configuration using a Web Browser Chapter 5
80 VideoJet 8000
MPEG-2 profiles configuration
Individual settings in a profile can be changed, and the modified profile can be
saved under a new name.
Warning!
The profiles are rather complex. They include a number of parameters that
interact with one another. Therefore it is generally best to use the default
profiles. The profiles should only be changed after you are familiar with all
the configuration options.
Profile name:
You can rename the profile. Afterward, the name will be shown in the list of
profiles that can be selected for each encoder.
Data rate:
The data rate for the speed of transmission over the network is shown for each
parameter value. You can change the data rate and decide whether you prefer a
constant rate or consistent image quality.
Selecting constant means that the data will always be transmitted at the set rate,
but the image quality may vary. Selecting variable means that the image quality
will be consistent, but the data rate can vary from the set value.
GOP structure:
In MPEG-2 encoding, image sequences are divided into groups (GOP – " G roup
o f P ictures"). Each group can contain three different frame types. I-frames
contain the complete information for an image and therefore require the most
coding data. P-frames code only the difference between the current image and
the previous one. These require considerably less data. Lastly, B-frames encode
only the difference between the current image and the previous and next images.
The require the least data. However, B-frames have a large delay, because
image information from subsequent images is required for encoding. Each GOP
always begins with an I-frame.
Note
B-Frames have a large delay and are not suitable for some applications,
such as manually controlling a dome camera. Keep this in mind when
choosing a GOP structure and length.