Vid Conf FAQ

1. Source
2. Translation
3. Destination

1. Source: A video camera and microphone are the canonical signal sources but any devise  capable of generating a video or audio signal  can theoretically be routed to a CODEC.  

• Video Camera: A video camera operates much like a television running in reverse. Inside a camera, a light sensitive screen coverts red, green and blue light to electricity--white only for a black and white camera. The screen is continually swept  many times per second. The results of the sweeping action are sequenced according to one of several possible video standards and flow to the camera's video out socket. The video out is connected to the CODEC's video in socket. Some CODECs have a video camera built into them in the same way camcorders house both a camera and video tape recorder in the same box. 
• Microphone: A microphone operates much like a speaker running in reverse. Inside a microphone, a thin diaphragm flexes in the presence of sound waves. The diaphragm connects to a magnet wrapped by an wire coil. As the flexing diaphragm pistons the magnet back and forth, the coil generates an electric signal. The coil connects to the microphone's mic out socket. The mic out is connected to the CODEC's mic in socket.   
• Other Sources: Any device capable of generating a video or audio signal can be connected to a CODEC. Potential devices include: DVD players, video cassette players, CD players, audio cassette players, musical instruments (electric) document cameras and computer based audio or video. Multiple devices can simultaneously feed a CODEC if they are routed through a mixer.   For example the source from a video cassette player can be combined with the images of people watching the tape along with their commentary to form the single feed going into a CODEC.   

2. Translation: CODECs are the loci of a Videoconferencing System. CODECs serve exactly the same function in video conferencing as MODEMs do in computer communication.

• Videoconferencing CODEC Unit: CODEC is an acronym for COmpression DECompression or COMpressor DECompressor. This neatly sums up a CODECs purpose.
• A CODEC compresses its video and audio input using mathematical algorithms. The compressed signal is made suitable for transmission over either computer (IP) or digital telephone (ISDN) lines. Each ISDN line is equivalent to two traditional ordinary analog lines. Multiple ISDN lines may be bound together for increased bandwidth. 
• Do not attempt to use a single analog telephone line for videoconferencing. The amount of bandwidth it supports is grossly inadequate for the task of meaningful video communication.  
• We feed our CODEC a video and audio signal from our cameras and microphones. The CODEC COmpresses and transmits it over the internet or digital phone lines while simultaneously DECompresses the incoming video and audio signal so that it can be viewed on a display.
• The CODECs at each site handshake with one another to establish a videoconference. Once that is done, each CODEC simultaneously transmits proximal and receives distal data. The data from the distal site is converted back to ordinary video and audio data by passing it through the inverse of the algorithm thru which it passed in the distal CODEC.

3. Destination: The signal from a CODECs video and audio out are routed to appropriate devices for viewing and preserving

• Viewing devices:
• Video Monitor (TV). Traditional CRT based monitor or alternate technology such as plasma display, LCD or front or rear screen projector. 
• Computer monitor.
• Preservation devices: VCR, DVD burner, video CD burner

• Videoconferencing now allows three or more sites to connect at once through the use of a video bridge called a Multi-Point Control Unit (MCU). Although this type of hardware can be expensive, certain applications, such as distance learning to multiple classrooms, can be more effective in a multi-point configuration.