1. A reproducing apparatus for reproducing an audio-visual stream file using a first data group recorded on a first recording medium and a second data group recorded on a second recording medium different from the first recording medium, the reproducing apparatus comprising: circuitry configured to: transmit to an external server via a network an identifier corresponding to a position in the first data group; receive from the external server a list of downloadable files corresponding to the identifier and in accordance with a date and time of the transmitted identifier; transmit to the external server a signal indicating a requested file from the list of downloadable files; acquire from the external server a manifest file containing recording medium path information indicating a path of a file contained in the second data group on the second recording medium, and virtual file system path information indicating a path of the file also contained in the second data group in a virtual file system, said file being an update file corresponding to the requested file and provides updated information not originally included with the first recording medium and included in the audio-visual stream; generate the virtual file system by mapping at least part of the second data group to the first data group in accordance with the virtual file system path information, said mapping including a conversion of file name of the file to a different file name, the first data group being managed in a directory structure containing an audio-visual stream directory managing the audio-visual stream file and a reproduction control file directory managing a reproduction control file as information for reproducing the audio-visual stream file; and reproduce the audio-visual stream file managed in the audio-visual stream directory of the virtual file system by having access to the file, in accordance with the recording medium path information and by having access to the file of the different file name via the reproduction control file managed in the reproduction control file directory of the virtual file system.