VBrick 6000 series Admin Manual page 39

Target Frame Rate
Frame Rate
Variation
Minimum Quality
Maximum Quality
Key Frame Interval In seconds. This interval allows an MPEG-4 player to "sync up" with a
VBrick MPEG-4 Appliance Admin Guide
• NTSC: Rate30, Rate20, Rate15, Rate10, Rate7.5, Rate6, Rate5,
Rate3, Rate2 and Rate1. Default = Rate30.
• PAL: Rate 25, Rate20, Rate12.5, Rate10, Rate5, Rate2.5, Rate1.
Default = Rate25.
This number represents how many frames the VBrick will send out
each second to carry the video to an MPEG-4 player. The word target
is used because the VBrick can vary its frame rate slightly in response
to the amount of motion in the movie or camera output. The
discussion of Rate Control Method goes into this in more detail.
Frame rate is the number of "frames" the VBrick sends in a second for
an MPEG-4 player to display. Moving pictures are made up of a rapid
series of "still" pictures that move so fast that the "illusion" of motion
is produced. A frame is one such "still" picture. Regular TV programs
in the U.S. run at about 30 frames in a second; and the more frames
presented in a second; the smoother the motion contained within the
video will appear. Encoding and transmitting a frame requires the use
of data, so that, when considering a particular bit rate, sending more
frames demands that each frame contain fewer fine details. Similar to
bit rate, the difference between "constant" and "variable" frame rate is
that if "constant" is chosen, then the VBrick will make a strong effort
to ensure that the chosen frame rate is reached as often as possible.
The "variable frame rate" setting allows the VBrick to change how
many frames it uses in a second (within limits of course), so that rapid
motion can play more smoothly.
Default = 0 (maximum smoothness). This number indicates to the
VBrick exactly how much it is allowed to vary its frame rate in trying
to reach its target bit rate. Decreasing this number means that motion
will appear smoother, but that the target bit rate will not be met as
closely. This option is used only VFR mode.
This number tells the VBrick appliance never to lose details in the
video beyond a certain level. Increasing the minimum quality ensures
that more detail will be seen, but that the trade off is that the target bit
rate and frame rate will not be met as closely.
This number tells the VBrick appliance never to include details finer
than a given level. Lowering the number can be useful for sending less
data when the subject matter of the video has little need for very high
"fidelity".
video stream already in progress by providing basic anchoring and
orienting data. If "key frames" are sent less frequently, it will take
longer for the video to begin playing after an MPEG-4 player is
started on a PC. Key Frames use up a lot of data, lowering the amount
of data available to carry the details of the video, so VBrick appliances
are often set up to send key frames at infrequent intervals.
MPEG-4 Configuration
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