QVidium QVENC Encoder v17 - Manual (Page 36)

User’s Manual v.17 QVidium
®
H.264 HD Video Codecs ™
Copyright 2011-2015 QVidium
®
Technologies, Inc. Page 36 of 73
ANC Data Line (default: line 9): This setting allows you to choose which video line within the
ancillary data of the SDI output the decoder will use to output the close caption data.
Genlock: By default, the decoder includes an IP clock synchronization and tracking mechanism
we call “genlock” to keep the decoder’s internal clock adjusted to track the frequency of the clock
from the incoming video stream. This clock tracking prevents the decoder buffer from overflowing
or underflowing, producing a smooth, fluid video signal. Genlock is enabled when the Genlock
parameter is set to either Loose, Normal (the default setting), or Strict. You can disable this
mechanism by setting it to Off. The Strict setting limits the maximum swings in frequency that the
adjustments can take with within the SMPTE ±30 ppm specification, but as a tradeoff, it can take
much longer to settle to the correct final frequency. The Normal setting is faster to settle than
Strict, but the frequency can change by as much as ±100 ppm.
Excessive packet loss can disrupt the ability of the Genlock mechanism to track the clock. In rare
circumstances, such excessive packet loss can cause the genlock mechanism to incorrectly
estimate the video clock frequency and result in the decoder losing color sync. Disabling Genlock
(by setting it to Off) forces the decoder to just rely in the internal, free-running crystal oscillator
within the decoder, and disables it from tracking the clock in the input video stream. Although this
crystal oscillator is very accurate, even small frequency differences between the clock of the input
stream and the crystal oscillator in the decoder can build up over time. After a period of time,
usually between 6 and 24 hours, the accumulated phase difference due to this small frequency
difference can cause the buffers in the decoder to overflow or underflow, thereby causing
occasional frame loss.
Error Handling (default: restart): Severe packet loss and mal-formed MPEG data may cause the
decoder to pause or stall. A software watchdog timer guards against these decoder error
conditions, and to Restart or Reboot the decoder, depending upon the Error Handling setting, to
insure 24/7 operation.
Check Audio Buffer (default: Yes): This setting enables or disables a failsafe mechanism that
responds to the the audio buffer going empty. Excessive unrecovered packet loss or jitter from the
network, or glitches in the SDI input of the encoder, can cause the audio buffer to run dry, causing
interruptions in the