User’s Manual QVidium™ StreamViewer
Page 8 © 2007 QVidium™ Technologies, Inc.
4.2
Starting Video Play Out
You may select from a number of convenient views of your list of profiles from the View
menu. To start receiving and playing out a stream for display in its own video window, just
double-click on the desired profile. Alternatively, you can start and stop play out by
clicking on “Start” or “Stop” under the
Stream menu.
4.3
StreamViewer Error Correction
StreamViewer supports some of the most advanced forms of live streaming video error
correction available, including the industry standard ProMPEG FEC (forward error
correction) and QVidium’s patent-pending Advanced ARQ (Automatic Retransmission
ReQuest). StreamViewer automatically detects and activates the appropriate form of error
correction based on settings at the video source.
4.3.1 ProMPEG FEC: Forward Error Correction
StreamViewer listens for ProMPEG FEC checksum packets and automatically configures
its FEC error correction mechanism accordingly, therefore eliminating the need for user
configuration of FEC. It automatically detects FEC settings, such as row and column sizes,
and uses the incoming parity packets to try and recover lost packets when necessary. The
Receive Stats panel, shown below, keeps track of lost and recovered packets, along with the
current FEC configuration, so you can monitor the effectiveness of the FEC settings.
4.3.2
ARQ: Automatic Retransmission Request
Automatic Retransmission Request (ARQ) tries to recover any packets lost during transport
by adding a small amount of delay, giving the decoder time to detect and request and
replace any missing packets with newly retransmitted ones. The size of this delay should
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 uninterrupted to the
MPEG decoder.
StreamViewer sends a small query packet upstream to the video source to automatically
detect and enable ARQ Mode when the video source supports QVidium’s ARQ. With ARQ
enabled and video play out started, StreamViewer 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 StreamViewer’s internal 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 three parameters that can be configured. In most cases the default parameters
should be adequate for the initial operation. The first parameter, Target Latency, specifies
the total delay, in milliseconds, allotted for the request, retransmission, and recovery
process. The ARQ mechanism will attempt as many retries as possible within this target
Manymanuals.com
Manymanuals.de
Manymanuals.fr
Manymanuals.it
Manymanuals.pl
Manymanuals.cz
Manymanuals.es
Manymanuals-pt.com
Commentaires sur ces manuels