User`s manual

14
AXIS 282/AXIS 282A - Video and Audio Streams
Notes: •MPEG-4 is licensed technology. The AXIS 282/AXIS 282A includes one license for the
decoder required for viewing in AMC. Installing additional unlicensed copies of this decoder
is prohibited. To purchase more decoder licenses, contact your Axis reseller.
•All clients viewing the MPEG-4 stream must use the same image settings.
Audio Stream Types
The three stream types for audio are:
• G.711 - International standard for encoding wired-telephone audio. Uses
PCM samples
to compress audio where higher signal values are compressed more than lower values.
In Axis products, this sets the coding type to μ-law 64 kbit/s.
• G.726 - Uses PCM samples to code the difference between
samples (ADPCM). Reduces
bandwidth without losing too much useful audio. In Axis products, this sets the coded
bitrate to 24 or 32 kbit/s.
All stream types are ITU-T standards and
operate on frequencies up to 4 kHz.
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 (Real-Time 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 which
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 alterna-
tive 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 con-
gestion. This is suitable for live video, as th
ere is no point in re-transmitting old infor-
mation that will not be displayed anyway.
• Unicasting is communication between a single se
nder and a single receiver over a net-
work. This means that the video stream goes independently to e
ach 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 simul-
taneously delivering a single stream of information to mul
tiple 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 routers.