Michael Derrer Fuchs/Shutterstock DVD and Blu-ray collections may still be a point of pride in many homes, with shelves or even entire walls adorned with movies and TV shows from across the decades. But what kind of condition are those discs in, and how long will they actually last? In general, DVDs and Blu-rays can last for years, or even decades, but that lifespan depends on the process used to make them and how they've been stored.  When DVDs first arrived in the 1990s, the promise seemed to be that these discs, like the CDs that came before them, were pretty much indestructible. Certainly, DVDs are easier to use than the VHS tapes they replaced, which often required fiddling with the VCR's "tracking" dial in a bid to reduce a jittery picture.…