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.
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.
Notes