When a program chain to be played is determined, a system controller
calculates the average bit rate in the program chain by dividing the
amount of data of the program chain by the total play time of the program
chain. The system controller also waits for a navigation pack to be
played and calculates the average bit rate in a video object unit in
accordance with a play time of the video object unit and the size of the
video object unit. When the average bit rate of the program chain is
greater than or equal to the average bit rate of the video object unit,
frame pause is performed. When the average bit rate of the program chain
is less than the average bit rate of the video object unit, field pause
is performed.