Capacity depends on the configuration, but generally you may have hundreds of simultaneous viewers up to the network bandwidth capacity of the system (e.g. 4 GBps)
For example, if you have a 1 GBps network and your video is encoded at 1000 Kbps then you can not have more than roughly 900 viewers (1,000,000,000 bps / 1,000,000 bps plus allowances for overhead, web page delivery, etc.).
The system puts no limits on the number of simultaneous viewers. Any dependancy is lead by network bandwidth and CPU performance.
Clustering increases capactiy because it performs load balancing
StreamPump increases capacity because streams may be delivered locally
Multicast from the server is supported for unlimited video delivery
At the touch of a button, an administrator can cause your live video, VoD content, web page, or text message to appear on one, some or all desktops and Digital Signage display stations without the viewer needing to do anything.