One of the major drawbacks of CD was its poor picture quality and the maximum resolution it supported for videos. As a storage medium also people were dissatisfied with only 700 MB. Some modifications were made to the storage mechanism of the CDs. Then single layer DVD was formed. Picture quality of DVD was a treat to watch compared to the one available on a CD.
Digital Versatile Disk or DVD supports 720x480, which makes the ratio of 1:5. It is an impossible ratio for movie viewing so normally the picture quality of DVD would suffer if any corrective measure is not taken. This is one of the common questions asked on the format. To get a proper answer we need to get into the DAR or Display Aspect Ratio. The resolution it supports is 16:9 and aspect ratio or AR of 720x576 for PAL disks. For NSTC, the aspect ratio is 720x480.
MPEG-2 video stream has something called DAR flag. The flag gives information to the player about the target display stream for which it has been encoded. There are four possible values, 16:9, 1:1, 4:3 and 2:11:1.
The picture quality of DVD suffers if the disk is wrongly put in incorrect output device. The picture is stretched, and the viewing is distorted. When the studios release the film in DVD format they create it in a certain resolution. What happens is, the studio converts the video into a certain format, and puts it into the disk to match its standard. Then the DAR flag is given the information to un-squeeze it again while playing the film.
While defining the picture quality of DVD, the term wide screen is often misrepresented. Letterbox and anamorphic are the two variants associated with the wide screen form. Letterbox is the process by which original aspect ratio is maintained while squeezing a different AR video into the disk.
The letterboxing process fails to take advantage of the available horizontal and vertical space of the screen. 16:9 ratios let the picture to show a black bar above and at the bottom of the video. However, when the same letterboxing is put in a 4:3 output device, like TV, the picture is shown as it is.
Letterboxing transfers cost quality. When the player is running a 16:9 disk the picture quality of DVD deteriorates a little. The change is unnoticeable to the human eyes if not observed minutely. Anamorphic DVDs contains 33 per cent more information than other wide screen DVDs. Therefore, when the picture is played on a Wide screen TV, the picture comes out in the original format.
When ripping the disk, picture quality of DVD can suffer a lot if certain aspects of the DVD are not taken into account. Ripping means converting the VOB and AC3 format into different format and muxing them into a container. More popular formats for mixing the video and audio from a DVD are AVI, MKV and MP4.
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