QVidium QVENC Encoder v17 - Manual (Page 63)

User’s Manual v.17 QVidium
®
H.264 HD Video Codecs ™
Copyright 2011-2015 QVidium
®
Technologies, Inc. Page 63 of 73
may help. The default value should be 300ms, but for operation over a WAN, we would suggest
increasing this value to 500ms or larger. Increasing this value will increase overall latency, so you
should minimize this value to minimize latency.
Out-of-Order buffer: When in ARQ mode, the decoder includes an optional additional buffer, in
addition to the Jitter Buffer, that reorders incoming packets in case the network is causing some of
the packets in the incoming video stream to arrive out of order. This buffer will re-order any
packets within it to be output in the order of the RTP sequence number. To enable this feature, you
must specify a buffer size in terms of the number of packets this buffer must hold until any packets
are output to the decoder. This feature is most useful if you choose to use Network Bonding on the
decoder which causes the outgoing video stream to be interleaved between the two Ethernet ports.
In this case, varying network delays may cause packets to arrive out of sequence, which this
feature helps to fix.
Detect video break: This feature only works for Network input. It monitors the PCR timestamps in
the incoming MPEG2 Transport Stream for discontinuities and unexpected values and then
automatically restarts the decoder when it detects a problem.
Detect video break limit: This parameter lets you set the minimum discontinuity time-out of
between 100ms and 2000ms (2 seconds). If the decoder detects a break in the incoming IP stream
larger than this value, then it will restart the decoder to prevent the decoder from getting into a bad
state.
ARQ Parameters
The parameters below ONLY pertain to QVidium ARQ error correction. They will be ignored unless
ARQ is selected for IP Transport.
Mode: Auto or Manual. In “Auto” mode, immediately after clicking on Start, the decoder sends out
a series of packets upstream to the encoder to measure the round-trip time and automatically set
the number of retries and round-trip time parameters based on the Target Latency parameter. The
results of these measurements can be seen in the decoder’s log file by clicking on Show Log and
scrolling towards the bottom of the log file. Clicking on Status will show the resulting value of these
parameter based on the measurements seen in the log file.
In “Manual” mode, the codec uses the Number Retries and Round Trip Time parameters to create
an ARQ buffer with the ARQ delay = Number Retries * Round Trip Time. In Manual mode, the
decoder’s ARQ mechanism ignores the Target Latency parameter and does not take any upstream
link measurements.
Target Latency: QVidiu m’s ARQ error correction operates through the addition of a small
additional buffering delay to provide enough time to request and receive replacement for each lost
packet. Target Latency gives the ARQ mechanism a target value for determining the necessary
ARQ delay. The ARQ divides the Target Latency, specified in milliseconds, by the round-trip time
to the video encoding source to determine the number of request attempts. Unless Robust Mode is
enabled, it sets a minimum ARQ latency of one round-trip time. A larger Target Latency allows the
system to increase the number or repeat requests, although the system will limit the maximum
number of retries to a maximum of 5, even if the Target Latency value would have otherwise
allowed more retries. Thus depending upon the Round-Trip time, the maximum delay may end up
being less than the specified Target Latency value.
Max Burst Drop: Burst packet losses are common occurrences in many IP networks and the
Internet. IP networks may dynamically change paths in response to load balancing, link failure
avoidance, and for other reasons. During a re-route, a sequence of queued packets on a
discontinued path may be dropped. A burst of packets may be dropped when higher priority
packets stall a lower priority buffer. ARQ will notice a burst packet loss when the first packet after