User’s Manual v.15
QVidium
®
H.264 HD Video Codecs
™
Copyright 2011-2014 QVidium
®
Technologies, Inc.
Page 24 of 71
UDP packet. All the other transport selections add an RTP header to the UDP packet stream. The
RTP header adds a timestamp and packet sequence number before inserting the MPEG-2
transport stream packets into the RTP/UDP/IP packet payload.
All of these transport types insert an integral number of 188-byte MPEG-2 transport stream
packets into the packet payload as specified by the TS packets per IP packet parameter. The IP
encapsulation adheres to the IETF/RFC 2733 standard for video over IP that specifies that the
packet payload must comprise an integral number of whole MPEG-2 transport stream packets
within an RTP header, so all transport types, aside from UDP-only, are compatible with the
ProMPEG Forum’s standard, SMPTE-2022, and the IETF/RFC 2733 standard.
3.5.2 Error Correction - ARQ: Automatic Retransmission Request
To enable
A
utomatic
R
etransmission Re
q
uest (ARQ), you must first select ARQ transport from the
Profile
dialog. ARQ transport must also be enabled at the decoder. With ARQ selected and the
encoder started, the encoder will begin to save outgoing packets for later retransmission, when
necessary. Normally, the ARQ port should be set to the same value as the outgoing UDP port for
the video stream, with a default value of 10000. This will allow the upstream ARQ retransmission-
request packets to travel back through most encoder-side firewalls without requiring any special
configuration at the encoder-side firewall. If you use a different ARQ port than video UDP port,
then you must also be certain to configure any encoder-side firewalls to allow the upstream ARQ
retransmission request packets through to the encoder. You may change the value of the ARQ
port, but the ARQ and UDP port settings must match on both the encoder and decoder.
At the receiver, the ARQ error correction mechanism first buffers incoming packets in a
synchronized network de-jitter buffer that maintains a constant, configurable delay for incoming
packets. The de-jitter buffer processes RTP sequence numbers and reorders packets as
necessary to restore proper packet sequence and to buffer against erratic network delays. Its goal
is to output a smooth, consistent flow of packets with increasing sequence numbers. This output
feeds the ARQ error correction mechanism.
The ARQ unit at the receiver watches for gaps in RTP sequence number from the de-jitter buffer
output, and immediately sends out retransmission requests when necessary. Incoming
retransmitted ARQ packets bypass the de-jitter queue and find their correct place in the ARQ
buffer, so that by the time packet are output by the ARQ buffer, the ARQ error correction
mechanism should no longer contain any missing packets.
When the encoder and decoder are both started, the decoder automatically measures the round-
trip delay and packet jitter to the encoder and automatically configures ARQ for optimal operation
according to a few basic user-specified parameters, as described in Section 3.5.2.
Note:
For testing ARQ error correction, select ARQ transport at both the encoder and decoder and
use the default ARQ parameters at the decoder (receiver).
3.6 Configuring Advanced Video Encoding Profiles
The encoder has a set of advanced configuration settings, configurable from the Advanced
Encoder Profile tab, as shown below in Figure 1b, and from the Advanced Network Profile tab as
shown in Figure 1c. The Advanced Encoding tab divides these parameters into 4 sections:
Audio/Video Encoding parameters, Control parameters, Output parameters, and File parameters.
All advanced IP/Ethernet network settings are located under the Advanced Network tab.
Warning:
Some combinations of parameters can cause the encoder to malfunction. QVidium does
not test, nor can it support, all possible combinations of parameters. Instead, we allow users the
flexibility of setting these parameters to suit their needs, and make the decision for themselves as
to whether the resulting operation meets the needs of an application. To get the system into a
