Digital Video (or Versatile) Disk (DVD)




Digital Video (or Versatile) Disk (DVD)

DVD is a standard format for distribution and interchange of digital content in both computer-based and consumer electronic products. The format enables storage of various types of large multimedia data on a new and improved version of CD (Compact Disk), which works on optical disk technology. That is, both DVD and CD store data by using pits embossed on a disk surface. However, these pits are about 4(1/2) times as dense on a DVD as on a CD, and can store about seven times more data per side. The greater density is due to a more efficient data modulation scheme and error correction method that packs more data bits into every inch. DVD follows Eight-to-Fourteen Modulation Plus (EFMPPlus) encoding as compared to Eight-to-Fourteen Modulation (EFM) encoding used bye CD.

Physically, both DVD and CD are identical in both diameter and total thickness. There are two variants of DVD- single-layer and double-layer disk. Single layer disk has storage capacity of 4.7GB, whereas double-layer disk has storage capacity of 8.5GB. A single-layer disk provides about 135 minutes of video playback at an average data rate of little less than 5 Megabits/second.

DVD standard has two layers of specifications known as physical layer and logical layer.

Physical layer specific apply to the physical media itself, whereas logical layer specifications are for supporting all types of applications. The physical layer specification defines following types of physical media:

1. DVD-ROM. Uses use it for mass distribution of pre-recorded software programs and multimedia.

2. DVD-RAM. Uses use it for general read-and-write applications in PC or consumer electronics domains.

3. DVD-R. Users use it for low-cost, write-once recordable media.

4. DVD-RW. It is a rewrite version of DVD-R.

On the other hand, the logical layer specification defines recording formats for video and audio data for mass distribution of pre-recorded motion pictures and music. key features of DVD-video and DVD-audio specifications are as follows:

DVD-video. DVD-video is now the most dominant movie storage format used. It allows storage of video in 4:3 or 16:9 aspect ratios in MPEF-2 video format using NTSC or PAL resolution. It may be of interest to note that NTSC has resolution of 720×480 and PAL has resolution of 720×576. The audio is usually Dolby Digital (AC-3) or Digital Theater System (DTS), and can be either monaural or 5.1 Surround Sound. In addition, it has multiple selectable language soundtracks and suitable, voice-over commentaries by the movie's cast or director, and convenient random access to special features.

DVD-audio. It offers multiple choices of sampling rate and number of bits per sample. For super-high fidelity, the music producer might opt for two channels with 24-bit sampling at a rate of 192 KHz. Contrast the basic CD standard with its two channels and 16-bit sampling at 44 KHz. The specification also supports up to six channels of multichannel surround sound with 24-bit sampling at a 44 KHz rate. Besides the improved audio features, DVD-audio specification goes beyond CD by making provision for visual museum, stills images, and video to accompany the audio program.

DVD has enough space to store movie and support multi-lingual subtitles, multi-lingual audio, multiple camera angles, etc. It supports region marking to protect against piracy and use of DVD from one region to another. It also supports Content Protection for Pre-recorded Media (CPPM) security technique to safe guard against copying, etc.