ere is almost no set-up time and subjects may be moving around from time to time this is particularly valuable. auto iris A process of correlating aperture size to the amount of light entering the camera. Auto Iris produces unpredictable quality in video production because white backgrounds or clothing will cause a camera to close down the lens when a person's face would be the desired gauge for the f-stop. Although it is a good feature in a videoconferencing camera, auto iris is not as effective as manual adjustment of the camera's iris in video production. Audio Video Interleaved. The filename extension for compressed video usually used under Microsoft Windows. AVI decompression usually takes place in software. AVI compression works on key frames to achieve the maximum possible entropy through redundancy elimination. After key frames are intra- frame compressed AVI then constructs subsequent delta frames by recording only interframe differences. AVI competes with MPEG-1 although MPEG-1 produces higher-quality video. Audio Visual Terminal. A term used in the ITU-T's H.320 specification. It refers to a videoconferencing Glossary of Terms implementation that can deliver an audio and video signal. American Wire Gauge, a standard measuring technique used for non-ferrous conductors (copper, aluminum). The lower the AWG the thicker the wire; 22 AWG cable is thicker than 26 AWG cable. Blue (as in RGB). B channel The ISDN circuit-switched bearer channels, capable of transmitting 64 Kbps of digitized information. B frame In MPEG, the B frame is a video frame that is created using bi-directional interframe compression. Computationally demanding, B frames are created by using I frames and P frames. Through bi-directional encoding the P (predictive) frame, which is created by using a past frame as a model, is compared an I (intraframe coded) frame: a frame that has had the spatial redundancy eliminated from it, without reference to other frames. Using interpolation the codec uses hints derived by analyzing past and predicte