In 1985-8 the CCITT specialists group on coding for visual telephony investigated a codec for videoconferencing and visual telephony at bit rates n*384 kb/s (n=1, . . ., 5) and down to 64 kb/s. The authors describe the video multiplex coder, which performs block addressing, video data encoding, formatting and serialization, video synchronization, motion vector coding, and insertion of side channels for indication of dynamic coding parameters. The transmission multiplex coder, which assembles the encoded video, audio, data and end-to-end signaling information and provides the user-to-network interface, is also considered.<<ETX>>