As Go Document Formats, So Goes Video

"To begin with, the hardware and storage media — magnetic tapes, disks, whatever — on which a film is encoded are much less enduring than good old film. If not operated occasionally, a hard drive will freeze up in as little as two years. Similarly, DVDs tend to degrade: according to the report, only half of a collection of disks can be expected to last for 15 years, not a reassuring prospect to those who think about centuries. Digital audiotape, it was discovered, tends to hit a “brick wall” when it degrades. While conventional tape becomes scratchy, the digital variety becomes unreadable."

http://www.consortiuminfo.org/standardsblog/article.php?story=20071223055232858