An ITU standard for splitting the video bandwidth in a videoconference into a conferencing channel and a media channel. It enables participants to share their computer screens or some other video source with all conferees. In a multipoint conference, the media channel is viewed by all participants, which is managed by the multipoint control unit (MCU).
The H.239 standard evolved from TANDBERG's Duo Video and Polycom's People+Content, which were proprietary methods used to add a data channel to a videoconference. See MCU
and videoconferencing standards