Adding Advanced Trickmode Functionality to Playlists
Using standard "trickmode" in fast forward and rewind operations enables users to view content at a faster rate than the normal speed of the video file. This is accomplished by having the server rapidly seek through the file and send appropriate frames to the client quickly. The seeking causes excessive disk I/O on the server and may cause bandwidth spikes between the server and the client.
The WMS Advanced FF/RW Format Media Parser plug-in reduces these disk I/O bottlenecks and bandwidth spikes by using a different process called advanced trickmode. This plug-in switches between various video files of the same content that were encoded at various speeds. So for every video file recorded at normal speed, there must also be several other versions of that video that were encoded at higher speeds (for example, 2x, 5x, and so on). Then, when the user wants to fast forward through a portion of a video file, Windows Media Player 9 Series or later sends the rate change to the server, and the server begins streaming a video that was encoded at that rate. If no video file was encoded at that rate, standard trickmode is used.
To use advanced trickmode, the WMS Advanced FF/RW Format Media Parser plug-in parses a file with a .tmi extension that contains information about the various video files and their corresponding rates. The .tmi file is an XML file that must reside in a server-side playlist because its MIME type is not recognized by Windows Media Player.
The following example shows a .tmi file that references the normal speed and 5x speed version of the same file.
<?tmi version="1.0"?> <tmi> <media src="file://C:\wmpub\WMRoot\1xfiles\myfile_1x.wmv" rate="1"/> <media src="file://C:\wmpub\WMRoot\otherfiles\myfile_5x.wmv" rate="5"/> </tmi>
The following example shows how to reference a .tmi file in a server-side playlist.
<?wsx version="1.0"?> <smil> <media src="E:\wmpub\WMRoot\trickfile.tmi"/> </smil>
The WMS Advanced FF/RW Format Media Parser plug-in is available only on Windows Server 2003, Enterprise Edition with Service Pack 1; Windows Server 2003, Datacenter Edition with Service Pack 1; Windows Server 2008 Enterprise; and Windows Server 2008 Datacenter.
For more information on the Advanced FF/RW functionality and how to properly encode video files to take advantage of it, see Understanding Advanced FF/RW in the Windows Media Services 9 Series Help documentation.