Multicast is a network delivery method where a single stream is sent once and received by many clients at the same time, rather than the camera sending a separate copy to each viewer (unicast). On a network that supports it, a camera publishes one multicast feed and every operator who tunes in shares it, so adding the tenth or hundredth viewer of a popular camera costs no extra camera bandwidth. ONVIF Profile S includes multicast where supported.
For surveillance, multicast's appeal is the video wall and large control rooms. When many screens need the same live feeds, unicast forces the camera or server to push N identical copies, and bandwidth multiplies with viewers; multicast collapses that to one flow on each network segment. This is why stadiums, transport hubs, and big command centres lean on it.
The pitfall is that multicast demands a network built for it. It depends on router and switch support (IGMP snooping, proper multicast routing) and does not naturally cross subnets or the public internet, so it shines on a controlled LAN and falls apart on a misconfigured or routed network — producing flooding, missing streams, or duplicate traffic. Many deployments deliberately stick to unicast for simplicity and use substreams plus a media server to manage viewer load, reserving multicast for environments engineered to support it.
