Decoder Set Up
This section provides details for advanced set up options for a VNC 200 decoder.
• Setting optimum playback delay — See “Setting Optimum Playback Delay”
• Monitoring bandwidth usage — See “Bandwidth Monitoring Page”
• Creation of custom output modes — See “Creating a Custom Output Mode”

Setting Optimum Playback Delay

During playback of a source stream, data is transported from a VNC 200 encoder across
the network and into a buffer on the VNC 200 decoder. Data is then read from the buffer
and output to the display. Because of the inherent time delay (latency) for data to be
transported across the network, it is not possible for the decoder to display the source at
exactly the same time as it is being encoded.
For this reason, the VNC 200 decoder imposes a playback delay to account for the total
data transit time. It also ensures smooth playback of a source stream by equalizing the
flow of data into and out of the decoder buffer.
Setting the playback delay too small may cause the buffer to “underrun” (data is read
from the buffer quicker than it can be written). This will result in the playback image
jumping as network loading changes.
Setting the playback delay too large will cause excessive image latency and may,
particularly on high bandwidth datastreams, cause the buffer to “overflow” (data is
written to the buffer quicker than it can be read). This will result in “jumpy” screen
updates and screen flashing.
NOTE: When a source has both a video and audio stream, these are treated
separately and can be subject to different processing delays. In many
applications, this will not present any noticeable issues. However, with some
source material, especially where correct lip-sync must be maintained, it may
be necessary to set different values for the video and audio playback delay.
The default playback delay is 0.1 seconds which will be suitable for most applications and
is the minimum recommendation for a 30 Hz source (or a 60 Hz interlace source). For a
60 Hz frame rate source, the minimum recommended playback delay is 0.05 seconds.
Valid playback delay settings can be determined by setting values then checking the
Pipeline Status Meter.

Bandwidth monitoring page

Playback delay is adjusted via the Bandwidth page for the VNC 200 decoder. This is
accessed via the video or audio hyperlink on the Display page:
VN-Matrix 200 Series • Advanced Setup Procedures 72