Communication method, communication system, and output equipment

In order to prevent interruption of processing at the time when the format of data changes during transmission of streaming data over an IEEE 1394 or other network, when streaming data output from first equipment is caused to be received by second equipment via a prescribed network, when the streaming data output from the first equipment changes from content A in a first format to content B in a second format, after the end of output of content B invalid data in the same format as content B is output, and during output of this invalid data the first equipment investigates the state of the second equipment (steps S 11 to S 14 ); when it is detected that preparations for input of streaming data in the second format are completed, output of content B in the second format is begun.