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About playlist elements

A playlist is composed of elements and their associated attributes. Elements are the building blocks that make up a playlist written in XML. Attributes are values that enable you to customize the behavior of the elements defined in the playlist. For example, you can use attributes to cause media elements to start based on the start or end points of other media elements. You can also use attributes to prioritize elements to ensure that some elements (advertisements, for example) are not interrupted by others.

The following table identifies the elements as they appear in the Playlist Editor. The phrase in parentheses identifies how the element would appear in XML syntax. The XML identification is used in the description.

Element Description
SMIL (smil) The smil element is the root element of any playlist. Synchronized Multimedia Integration Language (SMIL) is a XML-based markup language that Windows Media Services uses to construct playlists based on your input. The smil element is placed as the first element in your playlist. The smil element has the same behavior and attributes as the seq element. For more information, see smil element in the Playlist reference.
Media (media) The media element is the basic element in a playlist, used to represent the content you want to stream. A media element describes the location of the content and can include attributes that specify when the content should be played and for how long. A media element can refer to a file on a Windows Media server, an encoder stream, a remote stream, another playlist file, an ASP page on a Web server that generates a playlist, or a file on a third-party storage system. For more information, see media element in the Playlist reference.
Sequence (seq) The seq element is used to group a set of media elements into a continuous stream in which elements are streamed in order. Each media element within the seq element is streamed one after the other and their playback is synchronized with the presentation timeline, which identifies the start and stop times of each media element. For more information, see seq element in the Playlist reference.
Exclusive (excl) The excl element is used to group a set of media elements into a continuous stream in which elements have indeterminate start times and are not required to be played in sequence. The excl element is synchronized to the presentation timeline, which can be used to explicitly specify the start and stop times of the media elements. Unlike media elements contained in seq elements, the media elements contained within an excl element do not play unless they are explicitly started by either a programmatic event or the begin attribute. For more information, see excl element in the Playlist reference.
Priority Class (priorityClass) The priorityClass element is used with excl elements to group playlist elements into categories and define the rules for how playlist elements in each category can interrupt or be interrupted by playlist elements in other categories. For more information, see priorityClass element in the Playlist reference.
Switch (switch) The switch element is used to provide set of alternate elements. The server evaluates the possible alternatives in order and selects the first element that references content that can be streamed. For more information, see switch element in the Playlist reference.
Client Data (clientData) The clientData element is used to provide descriptive information and logging information about content items. This information can be displayed to users in their players. For more information, see clientData element in the Playlist reference.

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