DVD-Video info

Technical information about DVD-Video.

1. Introduction

DVD is not Digital Video Disc as many people think, but it stands for Digital Versatile Disc. The concept of DVD is quite similar as for CD. The main difference is that the laser for reading and writing uses a smaller light wavelength the information can be put with a higher density on the disc. A single-sided Single layer DVD can contain up to 4.7 GB of data, a double layer up to 8.5 GB.

DVD-Video is the official name of a DVD containing video, audio and navigational data with in a specified format, but just like everybody, we will use the term DVD here for DVD-Video. The main reason for its success on the market is that it was developed by a consortium of major consumer electronic manufacturers and with support of major film studios.

2. Characteristics

The main characteristics of the DVD-Video standard are:

Because the standard allows the use of very high bitrates for both video and audio, both picture and sound quality on a DVD can be superb. Support of more recent developments in audio technology like multi-channel, Dolby Digital and DTS have also enhanced the sound quality considerably.

Another difference with VideoCD and Super VideoCD are enhanced possibilities in navigation. This includes motion menu's, transitions and "on the fly" switching between multiple video angles, audio tracks and subtitles.

3. Disc structure

When you browse through the contents of a DVD you will see the following folders and files::

The .IFO files contain the navigational instructions and the .BUP files are actually backup files containing exactly the same data as the .IFO files.

The Video and Audio streams are in the .VOB files. You can actually play the contents of the .VOB files by opening them in a player like the Windows Media Player (if you do have an MPEG-2 encoder installed).

A DVD can also contain other files and folders for any kind of data, so you can actually make a DVD-Video and use it at the same time for data storage. On pre-recorded DVD's such files are usually intended for playback on a PC (special programs or games).

4. Copyright protection mechanisms

A lot of emphasis has been put on mechanisms to prevent unauthorized distribution and copying. There are three techniques.

Region codes

This mechanism was introduced to enable film studios to control the release of home video titles in different parts of the world. Most DVD players contain a code in its firmware which determines that only DVD's with the corresponding region code on the disc can be played. In total there are 6 different region codes for 6 different parts of the world. However, more and more you will find region-free DVD players in shops that will play DVD's with any region code.

Macrovision

Macrovision is aimed at preventing analog copying of DVD's. This software technology adds high frequency signals to the video output. These are not visible on TV or a computer screen, but a VHS recorder will be tricked by this signal. The results are colored stripes, distortion, rolling, black & white picture and luminance changes.

CSS

CSS or Content Scrambling System is the system to prevent digital copying. The data on the DVD is scrambled with this technology and the DVD player have hardware on board that descrambles the signal before sending it out. Already in 1999, the system was cracked by a 15 year old Norwegian boy who wrote a piece of software called DeCSS in order to be able to play DVD's under the Linux operating system. DeCSS has quickly spread all over the Internet and has created a big debate and many law suits between the film industry and people who defend that DeCSS cannot be illegal. The main argument that they use is that they have a legal right (Fair Use) to create a backup copy of a purchased DVD.

5. Recordable types

Currently there are several recordable DVD types suitable for DVD-Video on the market.

DVD+RW was developed by a consortium of a number of companies including Philips, Hewlett-Packard, Sony, Yamaha, Ricoh and some others. The format was developed with specifications to be completely compatible with standalone DVD players and DVD drives. A DVD+RW can be rewritten (the claims is about 1000 times). Short after the launch also the DVD+R appeared on the market. It is the corresponding format which can only be rewritten once.

The DVD-RW and DVD-R format are not initially developed within the original DVD specification, but this was added later on. It has a number of technical limitations compared with DVD+RW. It's way of recoding data is based on a completely different principle.

More and more DVD burners appear on the market that can record on all available types. However, it is not unlikely that one of both systems (+ and -) is going to disappear.

6. Compatibility

DVD's can only be played on DVD players and on DVD drives in PC's if an MPEG-2 decoder installed.

This is not always the case with +R/+RW/-R/-RW types. Although their specifications fall within the DVD specifications, you will find that some DVD players will not always play all recordable types. This is caused by the fact that DVD players are sometimes produced with specifications a little outside the strict DVD specifications. Commercial DVD's are usually produced with tighter tolerances than prescribed by the DVD specification, which means that they will have no problems with prerecorded DVD's. DVD burners may just be inside the DVD specifications but outside the tolerances used by the manufacturer. There may even be a difference in compatibility between different brands of media in combination with players.

With the wider acceptance and use of recordable DVD's it can be expected that compatibility issues will slowly disappear.