Methods and apparatus are provided for supporting a variable-length transport packet in an Audio/Video (AV) communication system. Data to be transmitted is determined. It is determined whether a transport packet is the variable-length transport packet. A header having information indicating whether the transport packet is the variable-length transport packet is generated. When the transport packet is the variable-length transport packet, an optional header having length information of the transport packet is generated, and the data and the transport packet having the header and the optional header, are transmitted. When the transport packet is not the variable-length transport packet, the determined data and the transport packet having the header are transmitted.