Understanding Fast Cache

When used with the Windows Media Player 9 Series, Fast Cache provides a way to stream content to clients faster than the data rate specified by the stream format. For example, using Fast Cache, the server can transmit a 128-kilobits-per-second (Kbps) stream at 700 Kbps. The stream is still rendered in Windows Media Player at the specified data rate, but the client is able to buffer a much larger portion of the content before rendering it. This allows the client to handle variable network conditions without a perceptible impact on the playback quality of either on-demand or broadcast content.

This ability is useful in the following situations:

• When the available network bandwidth of the client exceeds the required bandwidth of the content; for example, clients that use a cable modem, DSL connection, or corporate intranets.
• When the network connectivity is intermittent or has high latency; for example, wireless networks.
• When the quality of the content received is of paramount importance; for example, businesses that provide pay-per-view movies.

You can configure the Fast Cache settings for your server on the Properties tab of your publishing point. For more information on these settings, see Enable Fast Cache and Limit Fast Cache content delivery rate.  Fast cache is supported by both the RTSP and the HTTP protocols. Clients that connect using the MMS protocol will not receive the stream using Fast Cache, but will instead receive the standard bit rate stream.

Notes

• When setting up distribution servers to use Fast Cache, use either the RTSPT or HTTP protocols to connect to the origin server. For more information about distribution servers, see Using distribution servers.
• The RTSPU control protocol is incompatible with the Fast Cache feature and is not available when Fast Cache is enabled.
• You can control the behavior of individual streams by adding Fast Streaming modifiers to the URL that a client uses to connect to the stream. For example, the WMCache modifier enables a client to use the Fast Cache feature when it uses the following URL format to connect to the server: http://servername/file.wmv?WMCache=1. You can also control the maximum bandwidth available to stream a file or live stream by using the modifiers WMBitrate and WMContentBitrate. For more information, see Controlling streaming behavior.
• The Fast Cache feature is only used by clients that connect to a unicast stream.
• If you are using Fast Cache with a server-side playlist, clients that connect to your server must use the RTSP or the HTTP 1.1 protocol to receive the benefit of the Fast Cache feature.
• If you define the src attribute of a server-side playlist media element as being a publishing point on the local server using the lpp:// syntax, you must enable or disable player caching on the source publishing point. Changing the setting of the Enable Fast Cache property on any publishing point except the source will not affect the ability of players to cache content.

Related topics

• Understanding Fast Streaming