Icecast is free server software for streaming multimedia.

Overview

Relaying is the process by which one server mirrors one or more streams from a remote server. The servers need not be of the same type (i.e. Icecast can relay from Shoutcast). Relaying is used primarily for large broadcasts that need to distribute listening clients across multiple physical machines.

Type of Relays

There are two types of relays that icecast supports.
The first type is when both master and slave servers are Icecast 2 servers. In this case, a “master-slave” relay can be setup such that all that needs to be done is configure the slave server with the connection information (server IP and port) of the master server and the slave will mirror all mountpoints on the master server. The slave will also periodically check the master server to see if any new mountpoints have attached and if so will relay those as well.

The second type of relay is a “single-broadcast” relay. In this case, the slave server is configured with a server IP, port and mount and only the mountpoint specified is relayed. In order to relay a broadcast stream on a Shoutcast server, you must use the “single-broadcast” relay and specify a mountpoint of /.

Setting Up a Master-Slave Relay

In order to setup a relay of this type both servers (the one you wish to relay and the one doing the relaying) need to be Icecast 2 servers. The following configuration snippet is used as an example:

<master-server>192.168.1.11</master-server>
<master-server-port>8001</master-server-port>
<master-update-interval>120</master-update-interval>
<master-password>hackme</master-password>

In this example, this configuration is setup in the server which will be doing the relaying (slave server). The master server in this case need not be configured (and actually is unaware of the relaying being performed) as a relay. When the slave server is started, it will connect to the master server located at 192.168.1.11:8001 and will begin to relay all mountpoints connected to the master server. Additionally, every master-update-interval (120 seconds in this case) the slave server will poll the master server to see if any new mountpoints have connected, and if so, the slave server will relay those as well. Note that the names of the mountpoints on the slave server will be identical to those on the master server.

Setting Up a Single-Broadcast Relay

In this case, the master server need not be an Icecast 2 server. Supported master servers for a single-broadcast relay are Shoutcast, Icecast 1.x, and of course Icecast 2. The following configuration snippet is used as an example:

<relay>
    <server>192.168.1.11</server>
    <port>8001</port>
    <mount>/example.ogg</mount>
    <local-mount>/different.ogg</local-mount>
    <relay-shoutcast-metadata>0</relay-shoutcast-metadata>
</relay>

In this example, this configuration is also setup in the server which will be doing the relaying (slave server). The master server in this case need not be configured (and actually is unaware of the relaying being performed) as a relay. When the slave server is started, it will connect to the master server located at 192.168.1.11:8001 and will begin to relay only the mountpoint specified (/example.ogg in this case). Using this type of relay, the user can override the local mountpoint name and make it something entirely different than the one on the master server. Additionally, if the server is a Shoutcast server, then the <mount> must be specified as /.
And if you want the Shoutcast relay stream to have metadata contained within it (Shoutcast metadata is embedded in the stream itself) then the <relay-shoutcast-metadata> needs to be set to 1.