Windows Media Player must buffer a certain amount of data before
it can start rendering
Using Fast Start enables your users to have a better experience when playing back your content. Users can fast-forward and rewind content without additional delay and rebuffering. A Player that connects through broadband networks start playing the content more quickly, making the experience much more like viewing a television program or listening to a radio broadcast. Users will notice that server-side playlists streaming from your publishing point switch smoothly and seamlessly between content items. Additionally, the pre-buffering of data makes the Player resistant to playback errors due to lost packets or other network issues.
The increased bandwidth that the Fast Start feature initially uses to send data to the Player can overburden a network if many Players connect to the stream at the same time. To reduce the risk of network congestion caused by the Fast Start feature, you can limit the amount of bandwidth the Fast Start feature uses to stream to each Player. For more information about limiting Fast Start bandwidth, see Limit Fast Start bandwidth per player (Kbps).