How Does a DVD Player Work?by Kate Evelyn
A basic way to understand how a DVD player works is to look at its predecessor, the record player. With a record player, you can actually see a needle reading the grooves in the vinyl. The DVD player uses the same principles with the added benefit of twenty-first-century technology.
Laser Reads the Disc
The data on a DVD is stored in divots in the layers of plastic. These are similar to the grooves on a record but are much more precise. DVDs may appear to made entirely of plastic, but inside the plastic coating is a layer of aluminum. This is necessary so that the laser inside the machine can shine light through the plastic and have it reflected back to a lens on the other side. This laser is very thin and precise, not like one you would use in a typical science class. The computer inside the DVD player, using a device called an MPEG-2 decoder, translates the data from the lens into audio and digital signals, which it then parlays to your television through the audio and video connection cables.
Motor Spins the Disc
If the disc simply sat stationary in the DVD player, the laser would not be able to read it properly. Instead, the machine's motor rotates it, and the player deciphers the data for the entire film by moving in a spiral from the inside to the outside of the disc. The speed at which it moves depends on the disc you're playing. If you're playing a "dual-layer" DVD, once the laser reaches the outside, it reads additional tracks by heading back to the middle of the disc.
Device Measures Tracks
The DVD player also has a device that controls tracking, moving the laser outward or inward as needed to stay in the correct spot on the disc. This system makes sure that the laser reads the right data at the right time. It's also the reason you can skip ahead to a new part of a movie just by pressing the "skip track" button on your remote. The device tells the laser where it needs to go.
Though a lot of people worry about scratches on the reflective sides of their DVDs, most of the data the DVD player reads is actually deeply embedded and closer to the label side of the disc. This is why you can sometimes fix small surface scratches in the reflective side just by filling them in or polishing the DVD. But damage the label side and your DVD is destined for the trash.