CDs are for music, DVDs are for video. If you order the CD you'll get music of the concert, if you order the DVD you'll get the video of the concert. Sounds pretty simple to me even though the cover art is the same. 1 + 1 = 2 (impressive, isn't it?), but I was good in math back in high school so maybe it's easier for me to distinguish between the CD and DVD more than most.
