Advanced Fast Start

Advanced Fast Start is designed to minimize startup latency in Windows Media Player 10 or later. Startup latency is the period of time starting when a viewer requests a stream by using the Player, and ending when the content begins playing. A number of factors can introduce latency, such as the speed of the client computer, the state of the network, the available bandwidth, and the Windows Media server configuration. However, the primary reason for startup latency is the delay caused by buffering on the client.

An adequate buffer size is essential for providing a good user experience. The client buffer stores streaming media data in memory so that the Player can maintain smooth playback of a stream. With inadequate buffer size, presentation playback can be uneven. The buffer is also used by codecs that decode a stream. When more buffer memory is available to codecs, the audio and video quality is improved.

The buffer size affects the amount of startup latency because a client cannot begin playing a stream until the buffer is full. The Fast Start feature in Windows Media Services reduces latency significantly by streaming the data at an accelerated rate until the buffer is full. However, the stream still cannot be played until that point.

Advanced Fast Start enables the Player to begin playing a stream before its buffer is full. As soon as the Player receives a minimum amount of data, it can begin playing a stream while its buffer continues to fill at an accelerated rate—a rate that is faster than the encoded bit rate of the content. When the buffer is full, acceleration stops and the Player begins receiving data at the encoded bit rate.

For Advanced Fast Start to work effectively, adequate bandwidth must be available above the encoded bit rate of a stream. For example, if 1,200 kilobits per second (Kbps) of bandwidth is available for an 800 Kbps stream, the Player can use an acceleration rate of 1.5 times the encoded bit rate. On the other hand, if no additional bandwidth is available, the Player must fill its buffer before it begins playing a stream and no benefit can be gained from either Advanced Fast Start or Fast Start.


To use Advanced Fast Start, it must be enabled on both the Player and Windows Media Services because it depends on communication between the two components when the Player initially requests a stream. Advanced Fast Start is supported by Windows Media Player 10 or later or by Windows CE 5.0 or later (using the HTTP protocol).

See Also


Fast Start
Enable Advanced Fast Start

Other Resources

Encoding content for Advanced Fast Start