Dvd player how does it work

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.

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. The greater amount of information stored on a DVD video is chiefly due to the smaller pit size and tighter track spacing, but another factor comes into play--namely, compression. This development is based on temporal compression that compares each frame of video to the following frame and only stores the changes in the scene. It stores a single frame in a delay so as to continually put out the background of a scene and have more room to store the changes in the scene.

MPEG2 also uses the discrete cosine transform, which takes images and finds their frequency and then compresses any repetitive frequencies. Video compression allows more room to store additional viewing options, a big part of what makes DVD such an incredible advancement in technology. Other options include the choice of wide or full-screen viewing, sound tracks in different languages and closed-captioned viewing.

DVD video can also let the viewer decide the rating, R or PG, thanks to preprogrammed scene cuts on the disc itself. Viewers can also opt to watch an uncut version of the film or see out takes from the original. All of these selections can be chosen at the start of the film. The DVD then makes seamless skips from one scene to the next in the arrangement the viewer has chosen.

The director and the producer decide upon the amount and type of options available, so each individual DVD may have some, all or none of these options. Another big improvement of DVD video storage is its line resolution, which is far greater than the resolution offered by laser disc media and almost twice the resolution of standard VHS videotape.

This resolution is dependent on the capabilities of the television monitor used, but the monitor need not have high resolution for the viewer to enjoy the benefits of DVD. One more advantage is that a DVD disc is not physically touched while it spins in the player, so there is no wear and tear or loss of fidelity over time. In contrast, videotapes do touch a playback mechanism and eventually break down, degrading the quality of picture. Because data is stored in a spiral fashion, users should avoid wiping the disc in a circular motion; when cleaning a disc, wipe from the inside radially out to the edge.

Compared to video tapes, the longevity and easier storage of DVDs makes them a much more reasonable and user-friendly media. Newsletter Get smart. Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Benjamin Britton, an associate professor and electronic artist at the University of Cincinnati, provides the following explanation:.

Get smart. Sign Up. Support science journalism. Knowledge awaits. So a MPEG-2 compression system is introduced. As this is used, the data will be encoded onto the DVD as elements of the changing frames. This has to be successfully decoded and decompressed by the DVD player.

The disc drive mechanism consists of a motor that will drive the disc in a circular motion. The mechanism will also have a disc feed — a loading tray that is used to accept the DVD from the user.

Thus the entire disc drive is basically a spindle that holds the disc and a motor that is used to circle the disc. The spindle is held in its position with the help of small gears and belts that are attached internally. Some players have an automatic feed system in which, there will be no tray. Instead the disc will be automatically recognized after inserting a part of it. The optical system mainly consists of the laser beam, lenses, prism, photo-detectors and also mirrors.

The output of this mechanism will be the input for the disc-drive. The laser beam will be a red laser diode which works at a wavelength of nanometers. The optical system also requires a motor to drive it.

The laser system and photo-detector is placed together on a single platform. The laser diode as well as other diodes is made with the help of glass. The PCB is similar to that of any other electronic circuits. After the outline has been drawn, the components must be soldered to their respective places. All this must be done in a very clean environment so that the board does not become contaminated by dust. All the primary components of the electronic circuit should be made out of silicon.

This laser will be reflected differently according to the change of pits and bumps. Though the laser hits a single spot, the DVD moves in a circular motion so that the entire area is covered. Mirrors are also used to change the spot. These reflected laser beams are then collected by a light sensor eg. In short, the optical system helps in converting the data from the DVD into a digital code. Thus the corresponding analog signal of the DVD is obtained.