A relay is a function in the SHOUTcast server that tunes in to another (SHOUTcast/Icecast/Cast) stream and sends out the same stream again on the server. Relays simply repeat the stream and are not able to change the content or bitrate of a stream.
To set one up:
Go to Settings in Centova Cast, then Mount Moints.
Select your stream (/stream by default) then Relaying, make sure the AutoDJ is turned off in the AutoDJ tab or it will not allow you to set it up.
Enter the url to relay.
This needs to be the full URL of the stream eg. http://hubble.shoutca.st:8411/stream/1 or http://hubble.shoutca.st:8411/; For SHOUTcast these typically end on /stream/x or ;, for Icecast they end with the name of te mount point (eg. /stream) and for cast they end in /streams/x (x is the bitrate/stream name)