How Advanced FF/RW works

When clients use Advanced FF/RW to fast-forward or rewind an on-demand video file, the Windows Media server receives a request that includes the following information:

• A rate request.
• The presentation time at which the client began fast-forward or rewind.

Instead of processing presentation data from source content disks to fulfill client requests (as in standard trick mode), the server responds by matching the client's rate request value to a compressed copy of the original source file. It then locates the first available key frame after the presentation time reported by the client and begins streaming the file copy to the client after that point. The file copy is compressed so that its reduced file size also reduces the total presentation time by the correct amount. On the client, data appears to render at the rate requested. However, the client is simply playing back the content stream from the server. After the client's Advanced FF/RW request is complete, the server seamlessly switches back the original source content file and resumes playback at normal speed.

Notes

• When a user clicks the Fast Forward or Rewind button in Windows Media Player, the implementation of Advanced FF/RW appears to be seamless: the file plays faster in the desired direction. Users may experience a slight readjustment of the video displayed as the Player locates the nearest key frame when the file is played. During Advanced FF/RW, no sound is played, although any sound data that remains in the client cache is played until it is exhausted.

Related topics

• Understanding Advanced FF/RW