Multipoint control method, apparatus and program

A multipoint control method performed by a multipoint phone connection system comprising a multipoint control unit to which one or more first communication network terminal apparatuses and one or more second communication network terminal apparatuses are connected through a communication path, the number of points at which the one or more first communication network terminal apparatuses are located being M (M is an integer of 1 or greater), the number of points at which the one or more second communication network terminal apparatuses are located being N (N is an integer of 1 or greater, M+N is K+1 or greater, K is an integer of 2 or more), the method comprising:

• a point selecting step of, for each time period, selecting, by the multipoint control unit, up to K points from among M points at which the one or more first communication network terminal apparatuses are located and N points at which the one or more second communication network terminal apparatuses are located, a bit stream input in each time period from each first communication network terminal apparatus to the multipoint control unit through the communication path being a bit stream including, as codes representing a sound signal, a monaural code obtained by coding a mixed signal of sound signals of two or more channels input to the first communication network terminal apparatus by a first coding scheme and an extension code including a code representing information corresponding to a difference between the input sound signals between two or more channels, and a bit stream input in each time period from each second communication network terminal apparatus to the multipoint control unit through the communication path being a bit stream including, as a code representing a sound signal, a monaural code obtained by coding a sound signal of one channel input to the second communication network terminal apparatus by the first coding scheme;
• a step of, for each time period, obtaining, by a decoding apparatus in each second communication network terminal apparatus, a decoded sound signal by decoding a monaural code in an input code representing a sound signal by a first decoding scheme corresponding to the first coding scheme,
• wherein the method further comprises,
• a step of, by a decoding apparatus in each first communication network terminal apparatus,
• for each time period in which the number of selected points other than said each first communication network terminal apparatus itself is one and input codes representing a sound signal is a pair of a monaural code and an extension code corresponding to a sound signal of one point, obtaining a provisional decoded sound signal by decoding the monaural code in the pair by the first decoding scheme, obtaining decoded difference information from the extension code in the pair, and obtaining and outputting two decoded sound signals from the provisional decoded sound signal and the decoded difference information,
• for each time period in which the number of selected points other than said each first communication network terminal apparatus itself is one and an input code representing a sound signal is one monaural code corresponding to a sound signal of one point, obtaining and outputting one decoded sound signal by decoding the one monaural code by the first decoding scheme, and
• for each time period in which the number of selected points other than said each first communication network terminal apparatus itself is two or more and input codes representing a sound signal are two or more monaural codes corresponding to sound signals of two or more points, obtaining and outputting two or more decoded sound signals by decoding each of the two or more monaural code by the first decoding scheme;
• and
• a bit stream generating step of generating and outputting, by the multipoint control unit, a bit stream for a selected first communication network terminal apparatus of the one or more first communication network terminal apparatuses that has two or more selected points other than a point of the selected first communication network terminal apparatus itself, the first bit stream including, as codes representing a sound signal, a monaural code of the two or more selected points other than a point of the selected first communication network terminal apparatus itself.