Custom Mode; Automatic Latency Control - VBrick 9000 Admin Manual

variability of the encoded frame sizes allowing the latency to be reduced. A Rate Control
Setting of 5 allows the encoding algorithm to create larger encoded frames when the content
requires those larger frames to optimize quality—hence requiring larger latency. A Rate
Control Setting of 3 is the default.

Custom Mode

Custom mode allows you to vary the presets for Gap (default = 620) and Overhead (default
= 50) to correspond to your exact needs. The Gap setting when using any mode other than
Custom are conservative numbers taking into consideration the starting template, specific
changes in resolution and frame rate for high definition encoding, rate control settings, audio
sample rate, and selected mode. It should be noted that low audio sampling rates will force
higher latency (greater Gap).
It is also possible that for certain extremely challenging content, the Gap may need to be
increased to allow high quality video on certain decoders. The need for higher Gap would be
indicated by the decoder dropping frames resulting in a jerky effect on the display device. It is
also true that if lower latency is required, and the content is not difficult or some video
degradation is permissible, lower gap settings should be used. If you elect to deviate
significantly from the video template settings, it may be necessary to change the mode to
Custom and tune the Gap and Overhead settings to achieve high quality video output. Some
general guidelines are:
• For a given resolution, higher bit rates will allow lower Gaps for a given Overhead.
• For a given bit rate, lower resolutions will allow lower Gaps for a given Overhead.
• For a given resolution and bit rate, higher frame rates will allow lower Gaps for a given
Overhead.
• If the IDR interval is increased, quality will be enhanced, but the Gap may need to be
increased for a given bit rate.

Automatic Latency Control

The
Automatic Latency Control
minimize the latency for particular content and configuration parameters. The latency control
values are set based on certain configuration parameters, notably the video template used. If
the configuration does not correspond to standard template values, the latency control may
be suboptimal—leading to dropped frames if too low and unnecessarily high latency if too
high. In addition, since the required latency is variable depending on content, the standard
latency control settings are relatively conservative.
The latency control feature may be used in two ways. First, it can be turned on after the final
configuration changes, including the overhead setting, have been made and while typical
content is being encoded. By observing the
page, you can then disable the latency control option and utilize the
to manually set the latency to a value which minimizes latency for a particular use case.
Mode
A second choice is to simply leave the
cases this will lead to an excellent viewing experience with minimal latency. The disadvantage
of using this setting is that if the content changes dramatically, it may take some time for the
algorithm to respond to the change.
174
option offers an easy way to adjust the gap settings to
PTS-PCR Gap
Automatic Latency Control
value reported on the configuration
transport stream
Custom
setting enabled. In most
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