Method of playing system stream files with different recording formats

A playback method used by a playback device that plays a system stream file including encrypted video information,

• the playback device including
• an individual decryption key that is owned individually by each of playback devices, and
• a common decryption key that is owned in common by a plurality of playback devices,
• the system stream file including
• a first system stream file configured to be played back using both the individual decryption key and the common decryption key, and
• a second system stream file configured to be played back using only the common decryption key among the individual decryption key and the common decryption key, the method comprising
• identifying, by a processor, whether the system stream file to be playback is the first system stream file or the second system stream file, in accordance with a file extension of the system stream file, and
• selecting, by the processor, a decryption process of the system stream file.