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AXIS 233D - Video Streams
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 protocol 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 when there is network congestion packets can be dropped without
slowdown of the live stream since the protocol does not require delivery of all
data. This is suitable for live video, as there is no point in re-transmitting old
information that will not be 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 a bandwidth-conserving technology that reduces bandwidth usage by
simultaneously delivering a single stream of information to multiple network
recipients. This technology is used primarily on delimited networks (intranets), as
each user needs an uninterrupted data flow and should not rely on network rout
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ers.
How to stream MPEG-4
Deciding on the combination of protocols and methods to use depends on your viewing
requirements, and on the properties of your network.
RTP+RTSP
This method (actually RTP over UDP and RTSP over TCP) should be your first
consideration for live video, especially when it is important to always have an up-to-date
video stream, even if some images do 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, for example.