Videotelephony

videoconferencingvideo conferencingvideo chatvideophonevideoconferencevideo callingvideo conferencevideo callvideo linkvideo telephony
Videotelephony comprises the technologies for the reception and transmission of audio-video signals by users at different locations, for communication between people in real-time.wikipedia
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Telepresence

immersiontelepresence systemtelepresence technology
Telepresence may refer either to a high-quality videotelephony system (where the goal is to create the illusion that remote participants are in the same room) or to meetup technology, which goes beyond video into robotics (such as moving around the room or physically manipulating objects).
A popular application is found in telepresence videoconferencing, the highest possible level of videotelephony.

Skype

SkypingSkype PreviewJosh Silverman
News media organizations have begun to use desktop technologies like Skype to provide higher-quality audio than the phone network, and video links at much lower cost than sending professional equipment or using a professional studio. Videotelephony was popularized in the 2000s, via free Internet services such as Skype and iChat, web plugins supporting H.26x video standards, and on-line telecommunication programs that promoted low cost, albeit lower-quality, videoconferencing to virtually every location with an Internet connection.
Skype is a telecommunications application that specializes in providing video chat and voice calls between computers, tablets, mobile devices, the Xbox One console, and smartwatches via the Internet.

Telehealth

telemedicinetele-medicinetelemedical
Although not as widely used in everyday communications as audio-only and text communication, useful applications include sign language transmission for deaf and speech-impaired people, distance education, telemedicine, and overcoming mobility issues.
Telehealth could include two clinicians discussing a case over video conference; a robotic surgery occurring through remote access; physical therapy done via digital monitoring instruments, live feed and application combinations; tests being forwarded between facilities for interpretation by a higher specialist; home monitoring through continuous sending of patient health data; client to practitioner online conference; or even videophone interpretation during a consult.

Closed-circuit television

CCTVvideo surveillancesecurity camera
Such an antecedent usually consisted of two closed-circuit television systems connected via coax cable or radio.
Though videotelephony is seldom called 'CCTV' one exception is the use of video in distance education, where it is an important tool.

Codec

codecsdecoderdecoders
The development of advanced video codecs, more powerful CPUs, and high-bandwidth Internet telecommunication services in the late 1990s allowed videophones to provide high quality low-cost colour service between users almost anyplace in the world that the Internet is available.
Codecs are used in videoconferencing, streaming media, and video editing applications.

Slow-scan television

SSTVslow-scan TVslow scan
At the dawn of its commercial deployment from the 1950s through the 1990s, videotelephony also included "image phones" which would exchange still images between units every few seconds over conventional POTS-type telephone lines, essentially the same as slow scan TV systems.
Vostok was based on an earlier videophone project which used two cameras, with persistent LI-23 iconoscope tubes.

PictureTel Corp.

PictureTelPictureTel Corporation
One of the first commercial videoconferencing systems sold to companies came from PictureTel Corp., which had an Initial Public Offering in November, 1984.
PictureTel Corporation, often shortened to PictureTel Corp., was one of the first commercial videoconferencing product companies.

Project DIANE

Over the next 15 years, Project DIANE (Diversified Information and Assistance Network) grew to utilize a variety of videoconferencing platforms to create a multi-state cooperative public service and distance education network consisting of several hundred schools, libraries, science museums, zoos and parks, and many other community oriented organizations.
Project DIANE, an acronym for Diversified Information and Assistance NEtwork, was a very early videoconferencing based community service network created in the United States.

CU-SeeMe

CUSeeMeTim Dorcy
In 1992 CU-SeeMe was developed at Cornell by Tim Dorcey et al. In 1995 the first public videoconference between North America and Africa took place, linking a technofair in San Francisco with a techno-rave and cyberdeli in Cape Town.
CU-SeeMe (also written as CUseeMe or CUSeeMe depending on the source) is an Internet videoconferencing client.

List of video telecommunication services and product brands

List of vpopular instant messaging programsList of webcameras and videophonesList ofirst section
Webcams are popular, relatively low cost devices which can provide live video and audio streams via personal computers, and can be used with many [[List of video telecommunication services and product brands#Software Client brands|software clients]] for both video calls and videoconferencing.
This list of video telecommunication services and product brands is for groupings of notable video telecommunication services, brands of videophones, webcams and video conferencing hardware and systems, all related to videotelephony for two-way communications with live video and audio.

Mobile collaboration

Mobile collaboration systems now allow people in previously unreachable locations, such as workers on an off-shore oil rig, the ability to view and discuss issues with colleagues thousands of miles away.
Differing from traditional video conferencing, mobile collaboration utilizes wireless, cellular and broadband technologies enabling effective collaboration independent of location.

Distance education

distance learningcorrespondence courseonline education
Although not as widely used in everyday communications as audio-only and text communication, useful applications include sign language transmission for deaf and speech-impaired people, distance education, telemedicine, and overcoming mobility issues.
Web conferencing, videoconferencing, educational television, instructional television are examples of synchronous technology, as are direct-broadcast satellite (DBS), internet radio, live streaming, telephone, and web-based VoIP.

Personal computer

PCPCspersonal computers
Webcams are popular, relatively low cost devices which can provide live video and audio streams via personal computers, and can be used with many [[List of video telecommunication services and product brands#Software Client brands|software clients]] for both video calls and videoconferencing. In 1984, Concept Communication in the United States replaced the then-100 pound, US$100,000 computers necessary for teleconferencing, with a $12,000 circuit board that doubled the video frame rate from 15 up to 30 frames per second, and which reduced the equipment to the size of a circuit board fitting into standard personal computers.
In what was later to be called the Mother of All Demos, SRI researcher Douglas Engelbart in 1968 gave a preview of features that would later become staples of personal computers: e-mail, hypertext, word processing, video conferencing, and the mouse.

Discrete cosine transform

DCTiDCTinverse discrete cosine transform
The most important compression technique that enabled practical digital videotelephony and videoconferencing is the discrete cosine transform (DCT).
They experimented with the DCT and the fast Fourier transform (FFT), developing inter-frame hybrid coders for both, and found that the DCT is the most efficient due to its reduced complexity, capable of compressing image data down to 0.25-bit per pixel for a videotelephone scene with image quality comparable to an intra-frame coder requiring 2-bit per pixel.

Integrated Services Digital Network

ISDN ISDNISDN30
Only in the late 20th century with the advent of powerful video codecs combined with high-speed Internet broadband and ISDN service did videotelephony become a practical technology for regular use.
In a videoconference, ISDN provides simultaneous voice, video, and text transmission between individual desktop videoconferencing systems and group (room) videoconferencing systems.

UMTS

WCDMAW-CDMATD-SCDMA
In the present day standalone videophones and UMTS video-enabled mobile phones are usually used on a person-to-person basis.
The first national consumer UMTS networks launched in 2002 with a heavy emphasis on telco-provided mobile applications such as mobile TV and video calling.

Webcam

webcamsweb cameraweb cam
Webcams are popular, relatively low cost devices which can provide live video and audio streams via personal computers, and can be used with many [[List of video telecommunication services and product brands#Software Client brands|software clients]] for both video calls and videoconferencing. With the rapid improvements and popularity of the Internet, videotelephony has become widespread through the deployment of video-enabled mobile phones, plus videoconferencing and computer webcams which utilize Internet telephony.
Most webcams feature built-in microphones to make video calling and videoconferencing more convenient.

H.323

H323Registration, Admission and StatusH.323 Gateway
Videoconferencing in the late 20th century was limited to the H.323 protocol (notably Cisco's SCCP implementation was an exception), but newer videophones often use SIP, which is often easier to set up in home networking environments.
It is widely implemented by voice and videoconferencing equipment manufacturers, is used within various Internet real-time applications such as GnuGK and NetMeeting and is widely deployed worldwide by service providers and enterprises for both voice and video services over IP networks.

Video coding format

video coding standardsvideo codingvideo coding standard
The DCT algorithm became the basis for the first practical video coding standard that was useful for online videoconferencing, H.261, standardised by the ITU-T in 1988, and subsequent H.26x video coding standards.
For the spatial transform coding, they experimented with different transforms, including the DCT and the fast Fourier transform (FFT), developing inter-frame hybrid coders for them, and found that the DCT is the most efficient due to its reduced complexity, capable of compressing image data down to 0.25-bit per pixel for a videotelephone scene with image quality comparable to a typical intra-frame coder requiring 2-bit per pixel.

Multipoint control unit

MCUMCUs
Simultaneous videoconferencing among three or more remote points is possible in a hardware-based system by means of a Multipoint Control Unit (MCU).
A multipoint control unit (MCU) is a device commonly used to bridge videoconferencing connections.

IChat

iChat AVApple iChatchat software
Videotelephony was popularized in the 2000s, via free Internet services such as Skype and iChat, web plugins supporting H.26x video standards, and on-line telecommunication programs that promoted low cost, albeit lower-quality, videoconferencing to virtually every location with an Internet connection.
It added video and audio conferencing capabilities based on the industry-standard Session Initiation Protocol (SIP).

Sign language

sign languagesdeaf sign languagesigning
Although not as widely used in everyday communications as audio-only and text communication, useful applications include sign language transmission for deaf and speech-impaired people, distance education, telemedicine, and overcoming mobility issues.
One of the first demonstrations of the ability for telecommunications to help sign language users communicate with each other occurred when AT&T's videophone (trademarked as the "Picturephone") was introduced to the public at the 1964 New York World's Fair – two deaf users were able to freely communicate with each other between the fair and another city.

Lifesize

LifeSize Communications
In May 2005, the first high definition video conferencing systems, produced by LifeSize Communications, were displayed at the Interop trade show in Las Vegas, Nevada, able to provide video at 30 frames per second with a 1280 by 720 display resolution.
Lifesize is a video and audio telecommunications company in the United States which provides high definition videoconferencing endpoints and accessories, touchscreen conference room phones and a cloud-based video collaboration platform.

Video codec

codecvideo decodingcodecs
Only in the late 20th century with the advent of powerful video codecs combined with high-speed Internet broadband and ISDN service did videotelephony become a practical technology for regular use.
Video codecs are used in DVD players, Internet video, video on demand, digital cable, digital terrestrial television, videotelephony and a variety of other applications.

Web conferencing

webinarwebinarsweb conference
It offers data streams of text-based messages, voice and video chat to be shared simultaneously, across geographically dispersed locations.