"The .sfk file is a picture of the audio waveform that you see on the timeline. It saves this file on your drive so that you can scroll through the timeline much faster instead of having to wait for the display to be created every time you scroll. Any file that contains sound will have a .sfk file created when it is used in any SONY media software program, ie. you'll get them from .avi files as well as from .wav files in both Sound Forge and Media Studio. You can delete them if you wish, but they will be created again the next time you use the media file."