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AXIS 231D+/232D+ - Video Streams
When using MPEG-4 it is also possible to control the bit rate, which in turn allows control
of bandwidth usage. CBR (constant bit rate) is used to achieve a specific bit rate by varying
the quality of the MPEG-4 stream. When using VBR (variable bit rate), the quality of the
video stream is kept as constant as possible, at the cost of a varying bit rate.
How to stream MPEG-4
Deciding the combination of protocols and methods to use depends on your viewing
requirements, and on the properties of your network. The available options in AMC are:
AMC negotiates with the camera to
determine the transport protocol to use in the order
listed above. This order can be changed and the options disabled, to suit specific
requirements.
Unicast RTP This unicast method (RTP over UDP) should be your first
consideration for live unicast video, especially when it
is important to always have an up-to-date video
stream, even if some images are dropped.
Unicasting is used for video streaming,
so
that there is no video traffic on the
network until a client connects and
requests the stream.
Note that there are a maximum of 20
s
imultaneous unicast connections.
RTP over RTSP This unicast method (RTP tunneled over RTSP) is useful
as it is relatively simple to co
nfigure firewalls to allow
RTSP traffic.
RTP over RTSP over HTTP This unicast method can be used to traverse firewalls.
Firew
alls are commonly configured to allow the HTTP
protocol, thus allowing RTP to be tunneled.
Multicast RTP This method (RTP over UDP) should be used for live
multicast video. The video stream is always
up-to-date, even if some images are dropped.
Multicasting provides the most efficient usage of bandw
idth when there are large numbers of cli-
ents viewing simultaneously. A mult
icast broadcast cannot however, pass a network router unless
the router is configured to allow this. It is not possible to multicast over the Internet, for example.
Note also that all multicast viewers
count as one unicast viewer in the maximum total of 10
simultaneous connections.