A stream including plural access units is recorded on an information recording medium. Each access unit has a first packet that includes basic data as well as a second packet which includes extension data related to the basic data. The basic data is data that is decodable in a completed state without using extension data, and the extension data is data for improving the quality of data generated from the basic data. The header of the first packet holds first information, which indicates that the first packet includes the basic data, and the header of the second packet holds second information which indicates that the second packet includes the extension data. This arrangement allows a decoder that decodes only basic data to process the access unit, which includes the basic data and the extension data.