Reproducing apparatus, reproducing method, reproducing progam, and recording medium

For a large capacity recording medium, a user interface having high flexibility and enriched representation is accomplished. A flag that represents whether a play item has a multiple angle structure of which the play item is reproduced with a plurality of angles is described. In addition, a flag that represents whether the beginning of each decode unit is an angle switchable point is described. In a seamless multiple angle structure, the current angle can be switched without need to increase the number of interleave units. In a nonseamless multiple angle structure, with the flag, in a predetermined region on the rear end side of each angle, the current angle is prohibited from being switched. Thus, when a play item exits from the multiple angle, discontinuity in the reproduction can be prevented. In addition, with a flag that represents whether a sub play item should be reproduced not in synchronization with a main path, the sub play item of only audio data can be used as a BGM.