Abstract

In a teleconferencing system, a video encoder at the transmit end of the system includes a frame memory for storing video samples of a frame of a motion-picture signal and reading video samples at frame intervals. For still-picture transmission, an encoder circuit translates video samples read out of each successively shifted location of the frame memory which corresponds to at least one scanning line period of the frame into a signal representative of an intraframe correlation between adjacent video samples and generates a signal of a constant value during remaining line periods of the frame. For motion-picture transmission, video samples of the motion-picture signal for at least one scanning line period are translated into a signal representative of the intraframe correlation and video samples of remaining line periods of each successive frame are translated into a signal representative of the interframe correlation between successive frames. A video decoder at the receive end recovers a video sample from successively received intraframe correlation representative signals, delays it for a frame period to recover a video sample from the delayed sample together with a subsequently received signal which is the constant value signal during the still-picture mode and which is the interframe correlation representative signal during the motion-picture mode. The decoder further delays the last-mentioned video sample for a frame period to repeat the recovery process.