VBrick 9000 Admin Manual page 92

Field
Mode
Bitrate Mode
84
Description
Transport Stream only. Select from the following options. Note that
each transport stream mode is optimized for different applications. In
general a "variable" Transport Stream Mode (High, Med, or Low) is
more efficient than "constant" for network bandwidth because
transport stream null packets are not transmitted. If the variable
stream is ingested to a VOD server, the stream is converted to a
Constant bit rate file with null packets. As a result the storage
requirements on the VOD-W are roughly the same regardless of the
mode you select.
In the Constant and Variable (High, Med, or Low) modes, Overhead
and PTS-PCR Gap are automatically set to values that are optimized
for the current Video Resolution, Video Bit Rate, Rate Control
Setting, Audio Bit Rate, and Audio Sample Frequency. These
auto-selected values are shown as read-only in VBAdmin. In Custom
mode you can choose your own settings for Overhead and PTS-PCR
Gap but use caution because incorrect settings can result in poor
quality and dropped video frames.
• Constant – This mode will most likely be handled by an arbitrary
decoder and is the most universally recognized and utilized mode
for transport stream transmission. To maintain constant bit rate
over the network, null packets are added to the transport stream.
• Variable High Delay – Caps the overhead at a minimal value
thereby reducing maximum bursts at the cost of increased latency.
• Variable Medium Delay – Caps the short term bandwidth at the
same rate as a comparably configured constant bit rate stream but
average bandwidth will be lower because there are no null packets.
The latency is equivalent to the latency of a similarly configured
constant bit rate stream.
• Variable Low Delay – Provides a stream with the same average bit
rate as Variable High Delay and the latency is reduced but the short
term bit rate will have much higher bursts.
• Custom – Lets experienced users tune the algorithm-balancing
latency and delay for their individual stream characteristics and
application using Bitrate Mode, Overhead, and PTS-PCR Gap. The
values in the standard modes described above are relatively
conservative and it may be possible to tune overhead and latency
(PTS-PCR Gap) to lower values if content is low motion or if for
example, low latency is more important than video quality. Another
factor is Bitrate Mode: lower values for bitrate will allow more
aggressive tuning of the Gap and Overhead at the possible cost of
video quality (note that end-to-end latency is a function of network
delay and decoder behavior and the gap value generally sets only a
lower limit on overall latency). When switching to Custom mode,
the current settings for Transport Stream Bitrate Mode, Overhead,
and Gap are shown as starting points.
Read-only unless "Custom" Transport Stream Mode defined above.
Variable or Constant. Default = Variable.
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