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:
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.