User`s manual

User’s Manual v.13 QVidium

H.264 HD Video Codecs™

Technologies, Inc. Page 31 of 67

standard NTSC 29.97 frames per second, or 50 fields/sec for PALs 25 fps).

Low Delay: The QVPRO/QVDEC now includes a Low Delay mode that minimizes the “glass-to-

glass” latency from the encoder input to the decoder output, when Low Delay is selected on both a

QVidium QVENC, QVPRO, or QVSD encoder and a QVDEC or QVPRO decoder. Low Delay

mode on the encoder violates some of the usual MPEG buffering rules on the encoder in order to

minimize video latency. Therefore it may not work with third-party decoders, but requires another

QVidium decoder to properly decode the video stream. Minimum end-to-end latencies have been

measured at under 300 milliseconds. To achieve a consistent and minimum latency, please always

start the decoder before starting the encoder. If the video looks jerky in Low Delay mode, then you

must increase the DTS delay from PCR parameter on the encoder.

Video buffer size (ms): This parameter sets the size of an internal decoder buffer, specified in

milliseconds, to help improve the robustness of the decoder in handling network jitter and

interruptions. We generally recommend setting the Video buffer size to between 200 and 500 ms.

For low-latency applications, you can try setting it as low as 50 ms. For maximum robustness, you

can increase this parameter to 1000 ms.

Disable Genlock: By default, the decoder includes an IP Genlock clock synchronization and

tracking mechanism to keep the decoder clock aligned with 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 Disable Genlock parameter

is set to False, the default setting. However, excessive packet loss can disrupt the ability of the

Genlock mechanism to track the clock. In rare circumstances, such excessive packet loss can

result in the decoder losing color sync. The Disable Genlock setting provide a means for disabling

IP genlock. The drawback is that disabling genlock can result in a slow accumulation of delay and

occasional frame loss.

Error Handling: 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 restarts or

reboots the decoder, depending upon the Error Handling setting, to insure 24/7 operation.