What is a key characteristic of multicast video?

Multicast video is distinguished by its ability to efficiently deliver content to a group of users simultaneously. This method allows a single stream of data to be sent from the source to multiple recipients, which is particularly beneficial for applications like live broadcasts or conferences where the same content needs to reach many viewers at once.

This approach contrasts sharply with unicast, where content is sent to one user at a time, meaning that each viewer would require their own unique stream, significantly increasing bandwidth usage. Options focusing on single-user delivery or content downloaded upon request do not align with the core functionality of multicast. Furthermore, the mention of guaranteed video quality is not an inherent characteristic of multicast video; rather, the quality can be affected by many factors, including network conditions and the configuration of the multicast setup. Thus, the ability to stream video content to a group efficiently is what makes option B the correct answer.