QVidium QVMP2C-1011 - Manual (Page 16)

User’s Manual v.28 QVidium™ MPEG2+4 Codec
Of the required parameters, the first parameter, Target Latency, specifies the total delay, in
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video/IP stream, leave this field blank. The decoder interprets the video and audio signals as
UDP/IP packets in all cases, regardless of the type of packet transport you select. Specifying UDP
treats the packet payload as raw MPEG-2 Transport Stream data. All the other transport types will
assume that the incoming packets have an RTP header at the start of the payload, as per
IETF/RFC 2733 and related standards.
The network interface to the decoder includes QVidium’s patent-pending synchronized network de-
jitter buffering mechanism. In the decode interface, you may specify a delay for this de-jitter buffer
in milliseconds. The decoder holds the specified number of milliseconds of packets to give the
decoder ample time to account for random delays and to allow the decoder to correct packet
ordering. The decoder uses RTP sequence numbers of incoming packets to insert incoming
packets into their proper place in the de-jitter buffer before releasing those packets into the MPEG
decoder. The de-jitter buffer also uses the RTP timestamp to synchronize the decoder’s network
clock with the video source to adjust the de-jitter buffer hold time.
3.4.2 ProMPEG FEC: Forward Error Correction
To enable ProMPEG Forward Error Correction (FEC), you must first select ProMPEG transport from
the Profile dialog. Also, ProMPEG transport must be enabled at the encoder as described in
section 2.4.2. With ProMPEG selected and the decoder started, the decoder will listen to additional
UDP ports as specified in the ProMPEG 3.2 standard for FEC checksum packets. The decoder
automatically configures the FEC decoding parameters from the incoming FEC checksum packets.
Therefore, aside from enabling ProMPEG FEC, the decoder requires no further configuration for
FEC.
Note: For testing ProMPEG FEC, select ProMPEG transport and enter UDP port number and IP
multicast address (only if multicasting) corresponding to the settings at the encoder. The jitter buffer
can be left at the default of 50 ms, unless you expect larger network jitter. Also, make certain that
ProMPEG transport has been selected on the encoder and configured as per Section 2.4.2.
Note for Firewalls: UDP ports at P+2 and P+4 must be opened to allow access to column and row
checksum packet. (P is the UDP port for the video stream.) By default, column parity packets are
sent on port 10002 and row parity on port 10004.
3.4.3 ARQ: Automatic Retransmission Request
Automatic Retransmission Request (ARQ) tried to recover any packets lost during transport to the
decoder by adding a small amount of delay at the decoder during which time the decoder would
have time to detect and request any missing packets. The size of this delay should also include
adequate time for the missing packet to be received and inserted into the play out queue so that the
video stream can continue to flow smoothly and unimpeded to the MPEG decoder.
To enable ARQ, you must first select ARQ transport from the Profile dialog. Also, ARQ transport
must be enabled at the encoder. With ARQ selected and the decoder started, the decoder will
watch for gaps in the RTP sequence numbers from the output of the jitter buffer. When it detects
missing packets, it sends retransmission requests to the encoder so that the encoder can quickly
resend any missing packets. Incoming retransmitted ARQ packets bypass the network 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 output of the ARQ buffer should no longer contain any missing packets.
The ARQ has five parameters that can be configured in manual mode: Target Latency, Burst
Drop
, Robust Mode, Number Retries, and Round Trip Time. In automatic mode, the
system automatically measures and calculates the Round Trip Time and Number Retries. In
most cases automatic mode and the default parameters should be adequate.