User Guide User guide

VN-MATRIX User Guide Section 4: Advanced Setup Procedures
I458GB issue 6 Page 75
Setting Optimum Playback Delay
During playback of a source stream, data is transported from a VN-MATRIX encoder across the
network and into a buffer on the VN-MATRIX 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 clearly not possible for the decoder to display the source at exactly the same instant as it
is being encoded.
For this reason the VN-MATRIX decoder imposes a Playback Delay to take account of 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 recommended for a 30Hz source (or a 60Hz interlace source). For a 60Hz 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.