"Learning to play badminton" 8DVD and 15VCD difference?

"Learn to play badminton," I see catalog of teaching pieces are the same content, but a nominal "Towards Physical Education CCTV popular version of the 2008 Olympic Games: Learning to play badminton (15VCD)", while another nominal "fitness popular version: learn to play badminton (8DVD) ", and VCD's more expensive, why? Please understand that friends answer this question, thank you!

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There is no need to buy the disc, the Internet can be downloaded.

Give you a badminton forum site, where you can download to "learn to play badminton," 45 sets

may be published in factory different