A playback apparatus for playing a digital stream in conjunction with an application, the application being executed in the playback apparatus, the playback apparatus comprising: a package management unit (24, 38) operable to generate package information by merging files recorded on a read-only recording medium and files recorded on a rewritable recording medium, in accordance with a merge management information file recorded on the rewritable recording medium, the merge management information file referencing files on the rewritable recording medium for merging with files on the read-only recording medium; a selection unit (24, 25) operable to detect a plurality of playable titles, each of which is a unit of playback, from the package information, and to select one of the detected titles as a current title; a processing unit operable to execute an application that is specified in the current title and that is included in the package information; a playback control engine (24, 32) operable to control playback of a digital stream in accordance with playlist information that is specified in the current title and that is included in the package information; status registers (PSR -PSR), each of which stores a parameter relating to a playback status of the digital stream; and backup registers (PSR -PSR), each of which saves one of the status registers (PSR -PSR), when a title is called, the playback apparatus characterized in that after the executed application requests the package management unit (24, 38) to update the merge management information file, by specifying a new merge management information file, the package management unit (24, 38) changes an attribute of the newly specified merge management information file and attributes of all the files referenced from the newly specified merge management information file to read-only before updating the package information, and the backup registers (PSR -PSR) are cleared, and after digital stream playback stops due to the selection of a new current title by the selection unit (24, 25), the package management unit (24, 38) generates new package information by merging files recorded on the read-only recording medium and files recorded on the rewritable recording medium, in accordance with the newly specified merge management information file, the generation of the new package information being performed in a time period during which the current title is switched to the new current title due to the selection of the new current title by the selection unit (24, 25) a package management unit (24, 38) operable to generate package information by merging files recorded on a read-only recording medium and files recorded on a rewritable recording medium, in accordance with a merge management information file recorded on the rewritable recording medium, the merge management information file referencing files on the rewritable recording medium for merging with files on the read-only recording medium; a selection unit (24, 25) operable to detect a plurality of playable titles, each of which is a unit of playback, from the package information, and to select one of the detected titles as a current title; a processing unit operable to execute an application that is specified in the current title and that is included in the package information; a playback control engine (24, 32) operable to control playback of a digital stream in accordance with playlist information that is specified in the current title and that is included in the package information; status registers (PSR -PSR), each of which stores a parameter relating to a playback status of the digital stream; and backup registers (PSR -PSR), each of which saves one of the status registers (PSR -PSR), when a title is called, the playback apparatus characterized in that after the executed application requests the package management unit (24, 38) to update the merge management information file, by specifying a new merge management information file, the package management unit (24, 38) changes an attribute of the newly specified merge management information file and attributes of all the files referenced from the newly specified merge management information file to read-only before updating the package information, and the backup registers (PSR -PSR) are cleared, and after digital stream playback stops due to the selection of a new current title by the selection unit (24, 25), the package management unit (24, 38) generates new package information by merging files recorded on the read-only recording medium and files recorded on the rewritable recording medium, in accordance with the newly specified merge management information file, the generation of the new package information being performed in a time period during which the current title is switched to the new current title due to the selection of the new current title by the selection unit (24, 25)