Mpeg-4 Protocols And Communication Methods; Axis Media Control; How To Stream Mpeg-4 - Axis 213 PTZ User Manual

MPEG-4 protocols and communication methods

To deliver live streaming video over IP networks, various combinations of transport protocols and broadcast
methods are employed.
• RTP (Realtime Transport Protocol) is a protocol that allows programs to manage the real-time
transmission of multimedia data, via unicast or multicast.
• RTSP (Real Time Streaming Protocol) serves as a control protocol, to negotiate the transport proto-
col to use for the stream. RTSP is thus used by a viewing client to start a unicast session, see
below.
• UDP (User Datagram Protocol) is a communications protocol that offers limited service for
exchanging data in a network that uses the Internet Protocol (IP). UDP is an alternative to the
Transmission Control Protocol (TCP). The advantage of UDP is that it is not required to deliver all
data and may drop network packets when there is network congestion, for example. This is suit-
able for live video, as there is no point in re-transmitting old information that is not displayed
anyway.
• Unicasting is communication between a single sender and a single receiver over a network. This
means that the video stream goes independently to each user, and each user gets their own stream.
A benefit of unicasting is that if one stream fails, it only affects one user.
• Multicast is bandwidth-conserving technology that reduces bandwidth usage by simultaneously
delivering a single stream of information to multiple network users. This technology is used pri-
marily on delimited networks (intranets), as each user needs an uninterrupted data flow and
should not rely on network routers.

AXIS Media Control

The recommended method of accessing live video (MPEG-4 and/or Motion JPEG) and audio from the AXIS
213 PTZ is to use the AXIS Media Control (AMC) in Microsoft Internet Explorer for Windows. This ActiveX
component is automatically installed on first use, after which it can be configured by opening the AMC
Control Panel applet from the Windows Control Panel. Alternatively, right-click the video image in Internet
Explorer.

How to stream MPEG-4

Your viewing requirements, and the properties of your network determine the combination of protocols and
methods used. Setting the preferred method(s) is done in the control applet for AMC, which is found in the
Windows Control Panel. When this has been set, AMC tests all the selected methods in the specified order,
until the first functioning one is found.
RTP+RTSP
This method (actually RTP over UDP and RTSP over TCP) should be your first consideration for live video,
especially to always have an up-to-date video stream, even if some images get dropped. This can be
configured as multicast or unicast.
Multicasting provides the most efficient usage of bandwidth, especially when there are large numbers of
clients viewing simultaneously. Note however, that a multicast broadcast cannot pass a network router
unless the router is configured to allow this. It is thus not possible to multicast over the Internet.
Unicasting should be used for video-on-demand broadcasting, so that there is no video traffic on the
network until a client connects and requests the stream. However, as more and more unicast clients
connect, the traffic on the network increases and may cause congestion. Although there is a maximum of
20 unicast viewers, note that all multicast users combined count as 1 unicast viewer.
RTP/RTSP
This unicast method is RTP tunneled over RTSP. This can be used to exploit the fact that it is relatively
simple to configure firewalls to allow RTSP traffic.
RTP/RTSP/HTTP
This method can also be used to traverse firewalls. Firewalls are commonly configured to allow the HTTP
protocol, thus allowing RTP to be tunneled.
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