The reason why a video management system needs to support multiple transmission methods is because networks are complex and IP video sources do not all transmit identically. Segments of a network do not all necessarily support multicast. For example, in a video surveillance system, some IP cameras could be located on the corporate LAN and others could be mounted outside where they transmit data over a wireless network without multicast support. In addition to this, in this same video surveillance system, even if most of the viewing stations are located in the corporate LAN with multicast support, some of them could be connecting to the system via the Internet, as illustrated in figure 3 below.
In this scenario, an intelligent video management system can handle recording from multicast- and unicast-enabled cameras, transform the unicast cameras into multicast cameras to ensure efficient bandwidth utilization for local users, and provide a unicast stream to the remote clients, all while using a single server.
This server, acting as a proxy, is another very important component in efficiently managing the video traffic over the network. Ideally, this server must be able to auto-detect the connection type of the camera or the viewing client. This way, if a user sometimes connects from the corporate LAN, and then other times connects remotely from home, where multicast video transmission is not available, the video management server will have the ability to detect the point of connection, and automatically provide the viewing client with the most optimal type of stream.
Also, another important functionality of the video management system is the capability to transform a unicast-only camera into a multicast camera. This is important not only for cameras streaming over wireless links, but also for MJPEG cameras as described earlier. Usually, this is done by the video management server that is capable of getting the unicast stream from the camera and creating a multicast stream for the clients.
Getting More with Multistreaming Capabilities
In IP video surveillance, multistreaming is defined as the capability for an IP video source to produce multiple video streams of the same camera at different video quality. For example, an IP camera could produce one video stream at 4CIF 30 fps and another video stream at CIF 10 fps. However, once again, an IP video source capable of producing multiple streams is not enough to get multistreaming support. The back-end VMS must be able to control those streams as well.
To that effect, a sophisticated video management system will offer the system administrator the possibility to easily and effectively configure the available video streams for different purposes, such as live viewing, live remote viewing (with reduced bandwidth), recording, or any other specific purpose.
A typical way of configuring a system would be to setup a stream for live viewing at CIF 30 fps for maximum fluidity and a second stream for recording at CIF 10 fps to save on the bandwidth, allowing all cameras to be recorded at the same time while a few cameras are being monitored in real-time. Of course, in addition to bandwidth reduction, using a second stream for recording will also bring savings in terms of storage.
More so, multistreaming is not limited to differentiating quality between live and recorded video streams as it can be used for many other purposes. For example, people could use it to record two different streams at different qualities for short (higher quality) and long (lower quality) term storage. The positive impact of this configuration on the bandwidth consumption is obvious when it comes to transferring the recorded video to a long-term storage medium. Recording two different streams does not require transferring the video from one place to the other.
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