In DVD (Digital Versatile Disc) video standards, interactive operations can be performed, that is, users can switch sound or subtitles when playing back AV (Audio Visual) content, such as a movie, recorded on an information recording medium (for example, see Non-Patent Document 1). More specifically, the user operates a sound switch button 11 or a subtitle switch button 12 of a remote controller 2 to switch sound or subtitles of AV content displayed on a display device 1 shown in FIG. 1. For example, if the user operates the sound switch button 11 when sound 1 is set in the initial state in the display device 1, sound 1 is switched to sound 2, as shown in FIG. 2.
AV content on DVD video is recorded in the form of an MPEG (Moving Picture Experts Group)2 program stream. In the MPEG2 program stream, as shown in FIG. 3, a video stream (Video in FIG. 3), a plurality of audio streams (indicated by Audio 1, 2, and 3 in FIG. 3), and a plurality of sub-picture streams (Sub-pictures 1, 2, and 3) are multiplexed such that the audio streams and the sub-picture streams are AV-synchronized with the video stream. The sub-picture streams (sub-pictures 1, 2, and 3) are streams in which bitmap images are run-length coded, and are mainly used for subtitles.
Generally, a plurality of audio streams are used for recording sound of different languages, and a plurality of sub-picture streams are used for recording subtitles of different languages. The user can interactively select sound or subtitles of a desired language by using the remote controller 2 while video is being played back.
The DVD video defines a table structure, provided to users, indicating the relationship between sound numbers and subtitle numbers for a plurality of audio streams (audio 1, 2, and 3) and a plurality of sub-picture streams (sub-pictures 1, 2, and 3) in a program stream.
FIG. 4 illustrates a stream number table indicating the relationship between audio signals and subtitle signals. In this table, the sound numbers are referred to as “A_SN (Audio Stream Number)”, and the subtitle numbers are referred to as “S_SN (Sub-picture Stream Number)”. In FIG. 4, each of the plurality of audio streams is provided with A_SN, and each of the plurality of sub-picture streams is provided with S_SN. More specifically, A_SN=1: audio 2, A_SN=2: audio 1, and A_SN-3: audio 3. Also, S_SN=1: sub-picture 3, S_SN=2: sub-picture 1, and S_SN=3: sub-picture 2. In this case, a smaller number of A_SN or S_SN indicates an audio signal or a subtitle signal to be provided to users with higher priority. That is, A_SN=1 is an audio stream played back as a default, and S_SN=1 is a sub-picture stream played back as a default.
More specifically, sound 1 played back in the initial state in FIG. 1 is audio 2, which is A_SN=1 (FIG. 4), and sound 2 played back after being switched from sound 1 in FIG. 2 is audio 1, which is A_SN=2.    Non-Patent Document 1: DVD Specifications for Read-Only Disc Part 3; Version 1.1