How DVDs Work Introduction:- It was the VHS tapes that conquered the residence in the video market, but now it was a time of DVDs that fully occupy the position of a VHS tapes.. Departing from tape to disc gave the pleasure of home theater to a major extent, and filled the world with a feature of exsiting home video at the home too. Here are the article which help you to learn about the following topics in a brief. 1.What a DVD consists of. 2.In what way a DVD player reads a disc. 3.What are the major thing to look for when you are going to buy a DVD player. 4.Some history about DVD player. DVD Disks DVD is a very interesting invention of modern technology and is very parallel to a CD, but as we compare DVD with a CD it has a much bigger data capacity. When we take a typical DVD it hold about seven times more data than a CD contain. When we see the huge capacity on DVD it means that a DVD has sufficient room to store a full-length movies, MPEG-2-programmed movie, as well as we store a lot of other information too. Now we see the some of the typical contents of a DVD movie:- It contain Upto 135 minutes of high-quality video, in a format of letterbox or pan-and-scan format, with a 720 dot of horizontal resolution (When we discuss about the compression ratio of video it is about 40:1 using MPEG-2 compression.) When we discuss about the audio capability it was obtainable in up to eight languages using 5.1 channel Dolby digital surround music and Subtitles upto 32 languages. In case of DVD it can be used to store approximately eight hours of CD-worth music per side. The format of DVD is very different as we compare to the VHS tapes: 1.The picture quality of DVD is better as compare to VHS tapes. 2.Almost all the DVDs have a Dolby Digital or DTS sound of best quality, which is very similar to the sound you are going to experience in a theater. One of the interesting feature of DVD that it has an on-screen index,Means the maker of the DVD has paste many of the important parts of the movie, manytime with a picture icon. And when you use the remote and you select the part of the movie you want to view on DVD player, the DVD player will catch you exact to that part,and you does not need to rewind or fast-forward. DVD players are also compatible with audio CDs. Some of the DVD movies have both the option of letterbox format, which are going to fits wide-screen TVs, and the standard TV size format, In that case you can select in which way you want to see the movie. The movies on DVD have a number of soundtracks on them, so they can make available subtitles in different languages. The movies in english language may give you the option between the version dubbed into your own language, and provide the creative soundtrack with subtitles in your own language. DVD Layers As CDs DVDs have same diameter and thickness as CDs, and DVDs are prepared using some of the identical materials and manufacturing methods. As we see a data on a CD the data is encoded in the form of small pits and bumps in the track of CDs,in the same way the data on a DVD is also encoded in the form of small pits and bumps in the track of the DVDs. A perfect DVD is collection of several layers of plastic, calculating about 1.2 millimeters thick. Each layer of DVD is created by injecting the molding polycarbonate plastic. And the whole process forms a disc that contain a microscopic bumps which are arranged as a continuous, single and very long spiral track of data. When the clear and plain pieces of polycarbonate are formed, then the thin reflective layer is sputtered on top of the disc, by wrapping the bumps. Now the Aluminum is used at the back of inner layers,and the semi-reflective gold layer is used for the external layers of the disc, then we allowing the laser light to spotlight through the external and toward the inner layers. And when all the layers are made,the each layer is covered with lacquer, squeezed collectively and cured below infrared light.When we take a one-sided discs, the label is silk-screened on top of the nonreadable surface. On the other hand when we take a two-sided discs are printed only on the nonreadable region near the hole in the middle.Now we see the Cross sections of the a variety of completed DVDs is look like this way: Each one of the writable layer of a DVD contain a spiral track of data. On one-layer DVDs, the track provided are always circles from the inside of the DVD to the outside of the DVD. When the spiral track begin at the center It means that a one-layer DVD can be lesser than 12 centimeters. When you see the image to the right cannot make an impression upon us is how unbelievably tiny the data track is.It was only 740 nanometers that separate one track from the next (nanometer is avery small it was billionth of a meter).Now the lengthened bumps that are used to make a track are each 320 nanometers wide only, the dimension is only a minimum of 400 nanometers long and 120 nanometers high. The following figure give you the clear look through the polycarbonate layer at the bumps. Now you will learn about the "pits" on a DVD instead of bumps. Pits appear on the aluminum side, but on the other side that the laser reads , they are known as bumps. It was the microscopic dimensions of the bumps that make the spiral track on a DVD extremely long. If you are able to raise the data track off a one layer of a DVD, and extend it out into a straight line, then the size is almost 7.5 miles long. It means that the two-sided, two-layer DVD would have 30 miles of data that is almost 48 kilometres. When you try to read bumps then you an amazingly accurate disc-reading mechanism. DVD Storage Capacity There was a some reason that make DVDs better than CDs as respect to storage. 1. It has a higher-density data storage. 2.it contain Less overhead, and more area. 3.It has a multi-layer storage It has a higher-density data storage. When we talk about one-sided, one-layer DVDs it can store about eight times more data than from CDs. This larger area come on DVDs because pits and tracks on DVDs are very smaller in size. Now its time to learn how much extra data can be stored due to the presence of pits on a DVD. The track pitch on the DVDs is 2.16 times smaller, and the minimum length of the pits of a one-layer DVD is 2.08 times smaller than on a CDs.When we multiplying these two numbers given above then we find that there is room for about 4.5 times as many pits on a DVDs. Now where the rest of the increase come from? In the case of a CD,we find a lot of extra information that was encoded on the disc which permit for error correction .This information is only the reappearance of information that is already presence on the disc. The error correction method that is used on CD uses is very old and inefficient as compare to the method that are used on DVDs. In the case of DVD it doesn't waste as much space on error correction, It enable the DVD to store much more genuine information. There is one other way that DVDs attain higher capacity by encoding data on a slightly larger area of the disc than is made on a CD. Multi-Layer Storage When we increase the storage capacity of a DVD To a large extent , Then we increase layer of DVD up to four layers, two on each side of DVDs. On the DVD the laser that are used to reads the disc can mainly focus on the second layer through the first layer. Now see the list of the capacities of various forms of DVDs: It is amazing to see that the capacity of a DVD does not double when you plus a whole second layer to the disc. This reason behind this that when a disc is made with two layers, Then the pits have to be a slight longer, on each layers, than when a one- layer is used. This helps to neglect interference between the layers, this may cause errors when the disc is played in DVD player. DVD Video DVD Fact When you use a normal DVD movie that was not compressed, then it will take at least one year to download it from a normal phone line. Although the storage capacity of DVDs is very huge, and the video data that was not compressed would never fit on a DVD. If you want to make video movie fit to DVD, then you must need a video compression. There was a group called the Moving Picture Experts Group (MPEG).It established the principles for compressing of the moving pictures. When the video movies are going to put on the DVDs, they must encoded in MPEG-2 format and then they are stored on the disc and the compression format is a broadly accepted international standard. The DVD player contains an MPEG-2 decoder, which are not compressed this data as quickly as soon as you can watch it. The MPEG-2 Format and Data Size Reduction All the movie that are generally filmed at a rate of 24 frame/ second. This line we means that every second, there are accurately 24 complete images display on the movie screen. NTSC is a format that was used by American and Japanese television. Which display a total of 30 frames per second; but it does this in a series of 60 fields, every of which contains alternating lines of the picture. On the other hand other countries use PAL format, which display at 50 fields per second, but at the cost of higher resolution. Due to the differences in frame rate and resolution, an MPEG movie desires to be converted either the NTSC or the PAL system. The MPEG encoder that are responsible for the creation of the compressed movie file analyzes each frame and they decides how to encode it. This compression uses several of the technology as still image compression are used to eliminate redundant or irrelevant data. It may uses information from different frames to shrink the overall size of the file. Now each of the frame can be encoded in one of three ways given below: 1. As an intraframe It contain the entire image data for that frame. And this is the method of encoding provides the least compression. 2.As a predicted frame This frame contain a basic information which tell the DVD player how to show the frame based on the most freshly displayed intraframe or predicted frame. It means that the frame contains simply the data that relate in which way the picture has changed from the previous frame. 3. As a bidirectional frame When you want to display this kind of frame, then the DVD player must have the sufficient information from the neighboring intraframe or predicted frames.and by using this data from the nearby surrounding frames, it uses interpolation which calculate the exact position and exact color of each pixel. DVD Audio Now the DVD audio and DVD video both are different formats.Today the DVD audio discs and players are comparatively very less right now, and they will become more regular, and the difference in sound quality can be easily visible. If you want to take advantage of superior-quality DVD audio, then you need a DVD player that has a 192kHz/24-bit digital-to-analog converter (DAC). In market most of the DVD players are 96kHz/24-bit digital-to-analog converter. So in that case if you want to hear a DVD audio, then you like to have a DVD player with a 192kHz/24-bit digital-to-analog converter. As compare to CDs a DVD audio recordings can give better sound. Below are the chart that give the lists of the sampling rate and accuracy for CD recordings and the maximum sampling rate and accuracy for DVD recordings. In case of CDs it can hold 74 minutes of music. On the other hand DVD audio discs can hold 74 minutes of music at the rate of highest quality level, 192kHz/24-bit audio. When you try to lower either the sampling rate or the accuracy,Then the capacity of DVD increase and hold more music. In case of DVD audio disc it can store up to two hours of 6-channel,which is better than CD quality, 96kHz/24-bit music.When we Lower the specifications further, then the DVD audio disc can occupy roughly seven hours of CD-quality audio.  

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