The core technology used in a videoconferencing system is digital compression of audio and video streams in real time. The hardware or software that performs compression is called a codec (coder/decoder). Compression rates of up to 1:500 can be achieved. The resulting digital stream of 1s and 0s is subdivided into labeled packets, which are then transmitted through a digital network of some kind (usually ISDN or IP). The use of audio modems in the transmission line allow for the use of POTS, or the Plain Old Telephone System, in some low-speed applications, such as video telephony, because they convert the digital pulses to/from analog waves in the audio spectrum range.
The other components required for a videoconferencing system include:
• Video input : video camera or webcam
• Video output: computer monitor , television or projector
• Audio input: microphones, CD/DVD player, cassette player, or any other source of Pre Amp audio outlet.
• Audio output: usually loudspeakers associated with the display device or telephone
• Data transfer: analog or digital telephone network, LAN or Internet
Some observer argue that two outstanding issues are preventing videoconferencing from becoming a standard form of communication, despite the ubiquity of videoconferencing-capable systems. These issues are:
1. Eye Contact: It is known that eye contact plays a large role in conversational turn-taking, perceived attention and intent, and other aspects of group communication. While traditional telephone conversations give no eye contact cues, videoconferencing systems are arguably worse in that they provide an incorrect impression that the remote interlocutor is avoiding eye contact. Telepresence systems have cameras located in the screens that reduce the amount of parallax observed by the users. This issue is also being addressed through research that generates a synthetic image with eye contact using stereo reconstruction.
Bell Communications Research owns a patent for eye-to-eye video conferencing using rear projection screens with a camera behind it. This technique eliminates the need for special cameras or image processing.
2. Appearance Consciousness: A second problem with videoconferencing is being on camera, with the video stream possibly even being recorded. The burden of presenting an acceptable on-screen appearance is not present in audio-only communication. Early studies by Alphonse Chapin’s found that the addition of video actually impaired communication, possibly because of the consciousness of being on camera.
3. Signal latency: The information transport of digital signals in many steps needs time. In a telecommunicated conversation an increased latency, larger than about 150-300ms, becomes noticeable and soon unnatural and distracting. Therefore next to a stable large bandwidth, a small total round-trip time is another major technical requirement for the communication channel for interactive videoconferencing. (see ping time)
The issue of eye-contact may be solved with advancing technology, and presumably the issue of appearance consciousness will fade as people become accustomed to videoconferencing.
