Understanding playlists

Playlists provide a means of organizing different pieces of digital media content into a single user experience. Both client-side playlists and server-side playlists can be used with Windows Media-based content. For example, you can create a playlist using Windows Media Player (called a client-side playlist) composed of your favorite songs, and then shuffle and loop the playlist during playback. If you use a playlist with your Windows Media server (called a server-side playlist), you have the ability to stream multiple pieces of digital media content as you would with a client-side playlist, and you can use additional attributes to further control the behavior of the content. Client-side playlists created by the Player or by Web scripts are saved as Windows Media metafiles with an .asx file name extension. Server-side playlists that are created by content producers, server administrators, or Web page scripts are saved as Windows Media metafiles with a .wsx file name extension.

You can use playlists on a publishing point to accomplish several different goals —for example, to add advertisements, to switch between live and stored streams, or to dynamically respond to a user's demographic information. If you reference your content in a playlist, you can combine different Windows Media files into a single stream.

You can use a combination of server-side playlists and client-side playlists to provide a high degree of connection reliability for your streaming system. The client-side playlist can direct the player to the different Windows Media servers that are streaming the content, and the switch element in the server-side playlist on the Windows Media server can reference alternate content sources for the server. For more information on implementing this type of scenario, see switch element.  

Windows Media playlist files are Extensible Markup Language (XML) documents that are based on the Synchronized Multimedia Integration Language (SMIL 2.0) language specification.

By default, playlist files are Windows Media files with .wsx or .asx file name extensions. You can create playlist files by using the Playlist Editor on the Source tab or by using any text editor.

The section contains the following topics:

• About on-demand and broadcast playlists
• About wrapper playlists
• About creating and editing playlists
• About playlist elements

Notes

• For more information about the SMIL 2.0 Specification, W3C Recommendation, see the W3C Web site.
• If you have enabled the WMS NTFS ACL Authorization plug-in on either the server or a publishing point, every piece of content streamed by the server is authenticated against the user account. This means that if you are streaming content from a playlist, the user must be authenticated against every item listed in the playlist, not just the playlist file. If a user cannot be authenticated for an item in the playlist, that item is skipped.
• If you want to save playlist files to another computer or network drive, you must first grant write permissions to the Network Services account for that computer or network drive. For more information about how Windows Media Services uses rights, see Understanding rights.
• If you are using multicast distribution with your playlist file, you should only add content to a currently playing playlist if the content is in a known stream format. If the content is in a stream format that is not identified in the multicast information file, players receiving the multicast stream will be in an indefinite waiting state.
• If you are creating or editing server-side playlists using either a text editor or an automated script, make sure that you list the playlist elements and attributes in the correct case. Extensible Markup Language (XML) is a case-sensitive language, and Windows Media Services does not recognize any playlist elements or attributes that are not listed properly. For more information about playlist elements and attributes, see Playlist elements and Playlist attributes.
• If your playlist includes JPEG image files, do not include any syntax in your playlist that would cause the image to pause while rendering on the client's computer. Pausing a JPEG image in this manner can cause the player to enter a permanent wait state. If you must show a still image under these circumstances, create a video file of that image and then use the video file in the playlist instead.
• If your playlist includes JPEG image files and you are using the playlist file with a broadcast publishing point, be aware that users who connect to the broadcast while the JPEG image is being streamed will not receive the image. They will instead see a black screen. Once the playlist continues on to the next item, playback will continue as expected. If you want a JPEG image to be displayed for a certain period of time, you should use the repeatCount attribute to repeat the image for short durations that together equal the amount of time that the image is to be displayed. That way, players that connect while the image is being streamed can receive the image when it repeats. For example, if a JPEG image is to be displayed for 60 seconds, you could set a dur attribute value of five seconds and a repeatCount attribute value of 12. If a user connects two seconds into the broadcast, the image would be displayed after three seconds. If the repeatCount and dur attribute values were not used, the user would see a black screen for 58 seconds.

Related topics

• Playlist reference
• Sourcing from playlists, files, and encoders