DVD's or Digital Versatile Disks, Digital Video Disks
The What and How of DVD The How and What of CD-ROMS
 | Well, in a nutshell, a DVD stands for Digital Versatile Disc. It is a new standard format which at first glance has exactly the same appearance as a conventional Compact Disc. Unlike a CD, which has a maximum capacity of 74 minutes worth of digital audio, a DVD (dual-layer, dual-side) can hold a staggering 8 hours of near-broadcast quality video. So it's just like a laserdisc then? Wrong. Unlike laserdisc, a DVD disc is only 12cm in diameter, and has the massive advantage of being able to hold an entire movie on one side, meaning that you won't have to get up out of your comfortable chair half way through to turn it over. DVD discs can also have two layers on one side, and two sides. This gives loads of room available for extra features. |
| The most talked about application for the new standard disc is digital video. The goal of the entertainment and compact disc industries is to put a full length (over 2 hours) MPEG-2 compressed motion picture onto one side of a single CD-ROM. The current density or capacity of today's CD-ROMs does not allow for this. Currently, only approximately 75 minutes of MPEG-1 compressed full-motion video fit onto one "regular" CD. |
| The following is a summary of the most
common DVD capacities: - 4.7 GB (Single Layer Single Side) - 8.5 GB (Dual Layer Single Side) - 9.4 GB (Single Layer Double Side) - 17.0 GB (Dual Layer Double Side) |
| Therefore, the new DVD discs can store from 4.7 GB (single sided, single layer) up to 17.0 GB (double sided, dual layer per side for a total of 4 layers of information). Each layer of data on a DVD disc will allow up to 133 minutes of full motion MPEG-2 video. This amount of playing time will allow 95% of all movies to be contained on one side of a disc. This new disc will also support a variable bit data rate which will increase the quality of digital video playback thanks to a substantial buffer memory. The new DVD movie players are also capable of seamless switching between the two layers of information on each side of the disc. |
| Cutting a full 4.7GB single layer of a DVD disc today at the fastest encoding speeds available takes over 90 minutes. As the mastering software and hardware are improved, this time will decrease. Remember, a full DVD disc could contain up to four mastered layers of information. A mastering cut must be done for each layer of information put onto a DVD disc. Therefore, as the number of layers of information increases, so will the mastering cost and time. |
The How and What of : CD-ROMs