Simplified 6.3 Mbit/s codec for video conferencing

A color TV codec with a 6.3 Mbit/s transmission bit rate has been simplified by a newly developed coding method. This method is the combination of a 4-to-1 dot interlace system and 4 bit/pel DPCM. A digital filtering technique for reducing coding distortion is also employed. In comparison with an interframe codec having the same transmission bit rate, the amount of codec circuitry is halved. Subjective tests were performed to investigate the coded picture quality. It was found that this codec can present acceptable pictures for video conferencing, and that the picture quality for rapidly moving subjects is the same as that of the interframe codec operating at the same bit rate. A video conferencing system via a digital satellite link has been constructed for experiments by employing this codec. The experiments showed that the satellite link has a sufficiently low transmission error rate for the coded picture transmission. Moreover, it has been proved that transmission delay does not pose any problem for normal conferences.