In general, video telephony refers to visual communication using both video and audio transmitted over a communications network. It includes both mobile and stationary video telephony. Typically, video telephony refers to packet-switched and circuit-switched, wireless and wired, audio and video communications, such as voice over IP or VoIP communications, and video teleconferencing. Such applications facilitate remote communication by providing a visual image of each conference participant. Accordingly, video telephony allows parties to communicate audibly and visibly, without requiring lengthy and expensive travel. A videophone allows the transmission of video images over a standard telephone line. A fundamental problem associated with such transmission is the excessive frequency bandwidth of the video signal, as compared to the bandwidth of the telephone line. It is clear that video communication requires a relatively wideband channel, and telephone lines were not designed for this purpose. Full motion video and in particular full motion interactive video, requires the delivery of a very significant amount of data in a relatively uninterrupted stream. The standard two-wire telephone-set connection, referred to as the public switched telephone network (PSTN), is designed to exchange audio information, specifically voice, between two or more users. One way to solve this problem is to digitize the arbitrary signal (convert it to a stream of binary bits), and then transmit the digital data that result using a modem (modulator/demodulator). Modems can transmit digital data in the form of analog pulses through the essentially analog, band-limited telephone network. At the transmitter end, digital data is modulated into analog tones within the restricted bandwidth of the PSTN. At the receiver end, the analog tones are demodulated, the digital data extracted, and the arbitrary signal reconstructed.

More recently, data compression technology has facilitated the transmission of moving images using standard telephone lines. With the development of new compression techniques over standard telephone lines, it has now become possible to effectively transmit and receive video images over a standard telephone line. These data compression techniques have also been used to compress audio information, such as speech. Compressing both audio and video signal allows the information to be sent within the bandwidth constraints of conventional telephone lines. As a result, it is possible to transmit and receive telephone-quality speech and video images of adequate quality. Video compression is designed to represent full motion video with as small a number of information bits as possible, and still preserve acceptable quality. Acceptable quality is defined as the level of perceived quality required by the viewer of the decoded video. To preserve acceptable quality, many video compression encoders and decoders (i.e., video codecs) try to represent each frame of encoded video by predicting it from the previously encoded frame. For example, in a video telephone (videophone) application, it may be advantageous to have a coprocessor that performs certain MPEG-4 coder/decoder (codec) functions in particular ways. MPEG-4 is an International Standards Organisation/International Electro technical Commission (ISO/IEC) video and audio data compression standard developed by the Moving Picture Experts Group (MPEG). The MPEG-4 standard provides a set of tools and technologies enabling the integration of the production, distribution, and content access paradigms in such applications as digital TV, interactive graphics, and interactive multimedia. Generally, motion compensated prediction is used to reduce the amount of information needed to be coded for each frame. When motion compensated prediction is used between frames in a video sequence, the error in the prediction must be encoded and successfully transmitted to the decoder to preserve the quality of the decoded video sequence.

Video telephones typically consist of a video image capturing device, a standard video display unit, and the appropriate circuitry to provide video and audio communication between two like devices over a standard telephone line. In addition to technological developments in video compression that have contributed to the development of this growing industry. Other developments in imaging equipment have also contributed to the development of video telephones, such as the development of charge coupled device (CCD) and complementary metal oxide semiconductor device (CMOS) image sensors. A video telephone (videophone) uses a video camera in conjunction with a video display unit, a hands-free speakerphone, and a telephone interface. In a typical video telephony application, a camera is positioned to obtain an image of each of the video telecommunications session or interaction participants. The video camera lens is typically located in a fixed location allowing the user to move into or out of a fixed video scene. The captured video image of the video scene is delivered from the video camera device in the telephone unit across a wired network, such as the public switched telephone network (PSTN) to another receiving device that can display the image on a screen of a video display. CCD image-sensing devices are widely applied to image processing systems and digital signal processing systems, because they can serve as shift registers or sequential memory devices with high density. A CMOS image sensor employs a switching mode of forming a photodiode and a MOS transistor in each unit pixel on a semiconductor substrate using CMOS technologies. CMOS imagers have been increasingly used as low cost imaging devices. CMOS imaging devices offer improved functionality and simplified system interfacing.

Therefore, with the combination of the aforementioned technologies it is becoming commercially practicable to offer communication devices capable of capturing and transmitting video images and receiving and displaying video images to provide a video phone consumer product. Video phones for enabling both video and audio communications between users over a commonly connected telephone line are now used both in business and home. Home automation systems and video conference systems are communication systems that are closely related with those video phones. Video conferences provide the ability for persons at different locations to communicate without the need to travel to a common location to attend a meeting. With the thriving of the internet appliaction, video communication can be realized on the web. A web video phone or internet video phone, using a personal computer typically utilizes a web camera (webcam), microphone and speaker connected with the personal computer. The personal computer (PC) digitizes the audio and video signal, compresses this data and sends it over an Internet connection (LAN, WAN or modem) to a receiving device (typically another PC). The receiving PC decompresses the data and converts the digital data to an audio and video signal. This process occurs in both directions simultaneously.