You can use wrappers to provide advertisements or other content when users first connect to your server and/or when the content stream ends. When you specify a wrapper for your content, Windows Media Services includes that content as part of a wrapper playlist. A wrapper playlist enables you to insert your choice of opening and closing content as a playlist item before and after the primary content.
In addition to advertisements, content commonly streamed as wrappers includes dynamic playlists that are generated by Active Server Pages (ASP), site branding, and sponsor identification.
For example, a unicast client that connects to a live stream for which a wrapper advertisement was specified must first play back all of the content specified in the wrapper playlist before it can stream the live content.