 to reduce the number of network connections, or to reduce end-to-end delay. Use of the FlexMux tool is optional, and the FlexMux layer may be empty if the underlying TransMux instance provides adequate functionality. flicker An unwanted video phenomenon that results when the screen refresh rate is too slow or when the two interlaced fields that make up a video frame are not identically matched. Flicker is also known as jitter and sometimes as jutter. In the early days of television, interlacing two video fields to create a single video frame was used to combat flicker and eliminated it fairly well at rates over 40 fields per second. Flicker is not a problem with non-interlaced video display formats (those used for computer monitors). fluorescent lights Used for illumination in many corporate and public settings. These lights produce spectral frequencies of a less balanced nature than incandescent lights, and cause problems in a videoconference or video production process, and may cause 60 Hz flicker. footprint The primary service area covered by a satellite where the highest field intensity is normally in the center of the footprint, with intensity reducing toward the outer edges. format In television the specific arrangement of signals to compose a video signal. There are many different ways of formatting a video signal: NTSC, PAL, SECAM, component video, composite video, CD-I, QuickTime and SO on. forward motion vector Used in motion compensation. A motion vector is a physical quantity with both direction and magnitude; a course of motion in which pixels are the objects that Video Communication: the Whole Picture are moving. A forward motion vector is derived from a video reference frame sent previously. forward prediction A technique used in video compression. Specifically, compression techniques based on motion compensation in which a compressed frame of video is reconstructed by working with the differences between successive video frames. Frames per second. The number of frames contained in a single second