Windows Media Player 11 SDK Using Metafiles for Seamless Stream Switching 

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Using Metafiles for Seamless Stream Switching

You can facilitate seamless stream switching using metafile playlists. Usually, when a piece of content ends, buffering occurs for the next clip or stream before it opens (if it is content received from a streaming media server). Microsoft Windows Media Services enables you to eliminate, or at least minimize, this buffering time and have another piece of streamed content begin playing nearly immediately. The normal mode of operation for Windows Media Player is to open the next media stream referenced by the playlist 20 seconds before the end of the currently rendered stream. This generally provides a seamless transition between media streams, depending on other factors such as Web access times.

Use the EVENT element in a playlist in conjunction with OPENEVENT commands from the encoder to facilitate seamless switching between streams or files. Sending an OPENEVENT command 20 seconds or more prior to the EVENT command can minimize delays in stream switching. Then Windows Media Player is able to preload a portion of the upcoming streaming content into a buffer.

Use Windows Media Encoder to send a script command in the stream using the following format:

The event name must be the one defined in the EVENT element in the playlist. When Windows Media Player receives an OPENEVENT script command from the encoder, it looks to the EVENT element in the playlist and begins buffering the clip or stream defined in the EVENT element. Windows Media Player then holds this information until the actual event of the same name. When the named event is received, Windows Media Player switches to that previously buffered content.

Note   You cannot use Unicode characters for the OPENEVENT script command in the media file or the EVENT element in the playlist.

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