Feb 23, 2004 07:59 PM
8147 Views
(Updated Feb 24, 2004 12:27 AM)
DVD or digital video disk is the next evolutionary step for video storage and transmission. I am going to compare this format and media against traditional VHS (or VCR ) as it is known. DVD vs VCR is similar to CD vs Floppy in terms of capacity, quality and longevity.
Capacity: The DVD format allows one to store 4.5 to 7 Gigabytes of data. This basically allows you to have 5 to 6 medium res movies, or 1 high quality movie (upto 9 camera angles each with 525 lines resolution), 8 digital audio tracks and 32 subtitle tracks
The VHS on the other hand has one video track (250 lines of resolution) and 1 or two audio tracks (analog)
Longevity:
DVD uses an optical reader, which basically means that the drive head does not touch the disc surface. This allows it to have a lifespan of upto 200 years. They are also extremely durable and not subject to magnetic effects, accidental erasure, jamming, signal bleeds and so on. They can also be read infinite number of times without degradation of quality
VHS uses magnetic technology and is contact based reading/writing. This means, its max lifetime is 10-15 yrs before the prints start losing their quality.
Access:
DVD is by nature a random access device. Any point on the disc can be accesed instantly. VHS is serial access which basically means you have to rewind/forward the tape to reach a certain point.
Thus DVD basically destroys the VHS format which will soon be extinct.
However, here are some of the disadvantages, which will eventually be overcome with time:
- Standards:
Multiple DVD recording standards are in place (e.g: DVD-A, DVDRW+,DVDRW-) etc. which makes it difficult to select a player that can support all kinds of discs.
Difficult to record. You cannot record off the fly video onto a DVD, some intermediate processing (A-D conversion, encoding,encryption) is required.
DVD players are not cheap and widespread (yet !!)
To explore the true power of DVD, one needs superior home theatre equipment
Some people have requested additional technical details, so here goes .... most of this is available on the Net.
WARNING: Non-geeks and other regulars proceed at your own risk ....
Types of DVD: DVD-ROM, DVD-Audio, DVD-Video, DVD-R, DVD-RW (+ and -). Except for DVD-ROM, everything else uses the UDF file system.
DVD-Video is your basic and most common format for distributing video (or movies). It compresses the video using the mpeg2 format (which can preserve the quality of the original video). The audio is stored in PCM or AC3 format.. The DVD-Video usually has the following additional features:
CD quality surround sound
3-5 languages (audio) per title on each disk
135 minutes on 1 side of a single disk
Pan-scan letterbox and widescreen formats (to cater to different displays)
Parental locking
Country or region locking (i.e North american DVDs will not play in India and vice-versa)
Copy protection
Chapter division and menu based access.
Hope that is enough detail for everyone. The DVD Forum (dvdforum.org) publishes a bible that has more gory details, this was just a primer:
