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If you are pushing a stream to a Windows Media server and distributing it as a multicast stream, you must create an announcement (.asx) and multicast information (.nsc) file. The announcement is a Windows Media metafile that points players to the multicast information file. The multicast information file contains information that enables players to access and decode the multicast stream, including the IP address, port, and stream format information.
You can use the Multicast Announcement Wizard in the encoder to create the announcement, or you can create it on the Windows Media server. Creating the announcement on the encoder requires that you have access permission to the Windows Media Services service through DCOM. If you make any changes to the session configuration after you create the announcement, you must create another announcement before you begin encoding.
When you run the wizard on the encoder, you create the announcement file, multicast information file, and a Web page that contains an embedded player and a link to the announcement. You are asked to provide a name for the files and to save the files to a storage location that is accessible to players (or to a temporary location, if you plan to broadcast later.) The storage location can be either on your Web server for HTTP access or on a public share if you are providing access using a Universal Naming Convention (UNC) path. If you make the files available from your Web server, be sure to configure the Web server to either not allow caching of the file or to require a refresh check when cached by a client to prevent players from using multicast information that is outdated.
You have several options for making the multicast stream available to users. You can place a link to the announcement file on a Web page, make the announcement available on a shared folder, or send the announcement in an e-mail message. Users can access the announcement either by clicking the link to the announcement on a Web page or by opening the announcement directly. When a user opens the announcement file (.asx) in the player, the player extracts an URL in the announcement file; the URL points to the multicast information file. The player then downloads the multicast information file with the URL and begins playing the content.