Not sure about DVDs, but CDs weren't designed to last longer than 10 years. Most of my CD collection has physically rotted. Because I was using Windows Media Player and iTunes, I ripped most of collection in M4A format, which, at the time, was better than MP3. A couple of years ago, I decided that I wanted to re-rip my CD collection (some 200 odd CDs) in FLAC format instead of m4a format (don't ask). And some significant portion (50%?) of the new FLAC rips were missing tracks due to physical read errors on the original CD media.