written by: Debasis Das•edited by: Heather Marie Kosur•updated: 6/4/2010
DVD players are very handy gadgets that provide us hours of entertainment. It is getting easier to rent DVDs. Just shoving these shiny things into that player box gives us video playing out on our home theater TV or PC. How does the player do it all? How is the information recorded and recovered?
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There are two aspects to how a DVD player reproduces the content on a DVD. One is the mechanism of actually reading the content from the disc. This is part mechanical, part electrical/electronics, and part optical. The second part is entirely electronic and entails interpreting the data read and reproducing the video, audio, or the data that was originally written onto the disc.
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The Electronic Part of the DVD Player
The electronic part of the DVD player is the part that interprets the digital data recovered from the disc and produces the video. It could equally be true of audio data or computer written data. In each case, there are standards that govern how data should be formatted and written onto the disc, so that any compatible player can decode and reproduce the data.Let us talk about what functions you need in a video player as that is the most common use of the DVD player.
Video in digital form needs to be compressed to reduce the volume of data that straight conversion to digital produces. The prevalent standard has been the MPEG2 compression standard. MPEG4 is more recent. The player needs a decompression module to turn the compressed video into a straight uncompressed video stream in digital form. The TV to display the video can handle only analog video. US follows a standard named NTSC while many countries in the world follow PAL, and some countries follow the SECAM standards. You can choose the standard on most players or the selection could even be automatic.
The corresponding audio is also processed in parallel. The audio, too, follows certain standards such as the home theater 5.1 or the 7.1 or one of the various Dolby standards. So, at the output of the player, you get cables that let you connect the video to your TV video inputs. You can choose from CVBS, S-Video, Component, and, as is more common these days, HDMI. Component and HDMI produce the best quality. You really do not need to worry too much about these standards. You would typically have proper cables and properly marked inputs on your TV. The same is true of your audio, too. Just hook up the right cables to the TV inputs.
What the players need to ensure, additionally, is to enforce anti-piracy measures used by the content distributors. Content is scrambled when recording. This is known as the Content Scrambling System, or the CSS. Descrambling methods are known to your player maker if it has licensed the same. Thus, all movies and other content that are scrambled can be played by authorized players only. Players also have a region code to be handled. The DVD distributed in a particular country contains a specific region code and can be played by the authorized players in that country only. Besides, backward compatibility requires that older media such as the CD and the VCD be playable on the same player.
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Disc Reading Mechanism
A companion article on the history of the DVD player at Brighthub this month gives you details on DVD discovery and the details about capacity. A single-layer, single-sided DVD disc can record up to 4.7 GB while a dual-layer, dual -sided disc can hold 17.08 GB. This is usually rare; the more common high capacity form is double-sided, single-layer that can hold 9.4 GB of data. The data capacity increased as, rather than an infrared laser in CDs and VCDs,a red laser of smaller wavelength is used. This can read finer pits. For example, compared to the track pitch of 1.6 micron and the pit length of 0.8 micrometer in CDs, DVDs uses 0.74 micron track pitch and 0.4 micrometer pit length.
Data is read from the disc surface through a laser beam pointed at it. The surface has pits and no pits, small dips in the surface, to indicate the presence of bit of information or not. The organization is similar to what it was in the CD or the VCD or even the old Vinyl records (anyone remember them!). The laser (a pin in the case of the vinyl records) senses these pits arranged in a spiral. An electrical motor spins the disc, and a laser head is moves across the surface so that a laser can throw light on the surface through a lens system focused on this spiral track. The reflected light is then read to detect pit or not.