BridgeTech VB20 User Manual page 129

A list of detected PCR PIDs in the selected stream is shown together with their current
and maximum PCR jitter values. A PCR PID is selected for histogram presentation by
clicking the associated table entry. The histogram shows the number of received PCR
values versus jitter. PCR jitter is by default measured as PCR-AC for all interfaces. By
creating an ETR threshold template that enables PCR-OJ and assigning this template to
a stream it is possible to select PCR-OJ measurement mode by clicking the PCR_OJ
button.
The name of the current stream is displayed in addition to the two round-robin
indicator icons when relevant: the time cycle icon and the lock icon. By clicking the
lock icon the round-robin cycling is stopped or resumed. The pushbuttons Zoom in
and Zoom out enables rescaling of the graph. This makes it possible to view PCR jitter
values that are outside the range defined by the auto-scaling. Clicking the Clear
button will clear historical data from the histogram.
Tooltip functionality provides information about each histogram bar: the number of
samples, the percentage of total number of samples and the jitter interval
represented by the bar.
For PCR measurements to be valid it is essential that the signal be stuffed with null
packets (PID 8191) to obtain an absolutely constant bitrate. The stream info above the
histogram shows if the analysed stream contains null packets or not. A colour indicator
above the PCR jitter histogram indicates whether the signal is of constant bitrate or
not, as perceived by the PCR filter in the processing engine. Green indicates OK, red
indicates that the PCR jitter measurements are not valid due to the bitrate not being
constant.
Note that PCR jitter measurements for Ethernet streams are very sensitive to packet
loss, and packet loss results in a large jitter values - often for all PCR PIDs of an MPTS.
The PCR PID list displays the following parameters:
PID: The PID for which the following parameters apply.
Current: The last PCR jitter value measured.
Overall max: The maximum PCR jitter value measured from transport stream
Threshold: The PCR jitter threshold currently valid for the stream, as defined
In addition to the histogram itself, the following parameters are displayed:
Max jitter (ns): The maximum jitter value measured from the time the PID was
Average jitter
(ns):
Bin resolution
(ns):
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130
sync was obtained. Note that this may not correspond to the
maximum value for PCR jitter in the histogram, as the histogram
displays values measured from the time when a PCR PID was
selected.
in the associated ETR threshold template.
selected.
The average jitter in nanoseconds.
The width of the jitter interval spanned by each histogram bar.
PROBE USERS' MANUAL VERSION 5.0
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