A playlist identifies the items of content that can be delivered to a client and the order in which they must be delivered. For example, the following playlist instructs the server to send the client a Windows Media file containing an advertisement followed by another file containing a movie.
<?wsx version="1.0"?> <smil> <media id="media1" src="c:\wmpub\wmroot\ad.wmv" /> <media id="media2" src="c:\wmpub\wmroot\movie.wmv" /> </smil>
When a client connects to a Windows Media server and requests a playlist, the following actions are taken by the server and the playlist parser plug-in:
The server uses a file data source plug-in to read the playlist file into a buffer.
The server calls the playlist parser plug-in to create a playlist object.
The plug-in creates the playlist object, reads the buffer created by the server in step 1, and populates the playlist object with content items listed in the buffer. You can think of a playlist object as an in-memory tree structure that contains an ordered list of the media elements identified in the playlist file.
The server uses the playlist object to determine the order in which media elements must be streamed to the client.
The preceding example identifies a playlist written in the SMIL format. Windows Media Services contains a plug-in that parses the SMIL format. However, any format can be used as long as you create a custom playlist parser plug-in that can understand the format and convert it to SMIL so that the server can understand it. For more information, see Creating Playlist Parser Plug-ins.
A playlist parser plug-in can be enabled only for the entire server. You cannot enable one at the publishing point level.