The term DVD is a little vague with no one really claiming the definitive meaning, but the most commonly agreed term is Digital Versatile Disc.
It works like a Compact Disc (CD) in as much as a laser is used to read microscopic pits burnt into a chemical layer embedded in a sandwich of plastic. However the storage capacity of a DVD is approximately 5 times greater (in computer terms 4 gigabytes of data can be stored instead of 0.75 for a CD-ROM). This amount storage is doubled (8 gigabytes) by the fact that a DVD can have two layers of information. The second layer is read by refocusing and increasing the power of the laser (which your player will do automatically).
It is this increase in storage capacity along with improvements in information compression that has meant that not only high quality sound but high quality moving pictures can be stored on the format.
Superficially the DVD discs look like CD's, but they tend to be a little thicker, and while most DVD players can play CD's, CD players cannot read DVD's.
The information is stored on a DVD digitally as opposed to analogue, which means it is stored like computer data as a series of one and zeros rather than a wave form. This means that digital is very efficient and allows more data to be stored in the same space (and the information can be stored with a greater quality). It is also less prone to errors, as a stream of data can be checked and corrected as it is read in by a device.
DVD is not the only media to be digital. Most mobile phones are digital. CD's stores music digitally and that is why it sounds better than other earlier formats (there is of course also now MD's and DAT tapes which are also digital). Television is also moving from a broadcast analogue signal to digital (Sky and ITV digital in the UK).
So television is digital yes? No although the signal may be broadcast digitally it has to be converted back into an analogue signal to display on all current television sets, thus the need for a set top box. The same conversion also happens with the DVD player when it is linked to the television.
If the television is analogue why bother with a digital signal. When as previously mentioned digital is less prone to interference (due to error correction), and delivers higher picture quality. Therefore digital is good.
Ok DVD is digital but even then it has to be compressed to be able to get it to fit onto the disc. There is a lot of information contained in a high quality picture (just look how long it takes to load them over the Internet compared to text), and broadcast quality moving pictures require these pictures to change over fifty times a second. So the picture information must be somehow compacted to fit it onto a disc.
The standard used to achieve this is called MPEG2 encoding, and the way it works is quite clever. If you look at any two frames of a film, for the most part they will be the same, a person may have moved but the background is the same. The encoding processes notices this and only records the changes from the previous frame, thus saving a vast amount of space.
Is all encoding of video MPEG2? No there are many of different encoding techniques from the older AVI and MPEG1 (used by the Internet) to the even more efficient MPEG4. The agreed standard for DVD is MPEG2, and with the proliferation of hardware and software in this format it is almost impossible to be changed.
There are three main types of DVD players. Stand alone DVD players, Games consoles, and PC DVD drives.
These can either be portable (like a small laptop PC or organiser) or in a unit that looks like a CD player. The portable players usually have a small display or can be linked to a normal TV like the non portable types. The picture and sound quality of the non portables tend to be superior as they have to make less concessions due to size.
Such as the Playstation 2 or forthcoming X-Box are capable of DVD film playback. These devices store their games on DVD ROM and have TV output therefore it was an easy task for the manufacturers to include a movie decoder. These players do a good job of DVD playback however they lack the home cinema connectivity of a stand alone player.
DVD ROM drives are now common place in PC's. They are slowly replacing CD ROM drives as the standard. All of these drives when used in conjunction to either a hardware or software DVD movie player can be used to watch films. Of course by default the picture will be displayed on the computer monitor and the sound through the PC speakers. Although with a graphics card with a TV output and the sound card connected to either the TV or sound system things can be improved. The biggest disadvantage of this set-up is the picture and playback quality are not as good as a standalone player.
You may have noticed that while watching a film it will pause for a second about half way through. This is probably the layer change and it is quite normal. Due to the size of films even after compression the chances are once the menus, various sound tracks, and extras are added the film will be too big to fit on a single layer.
This means that part way through the film the laser has to refocus to read he other layer and this is not quite instantaneous.
No not the aqueous equivalent of Lassie, but DVD's that have information written on both sides of the disc. A few early discs were encoded like this, where instead of using two layers the two sides were used instead.
This proved to be a major pain as when the layer change is reached the disc has to be taken a out and flipped to watch the second half of the film (hence flipper). Luckily the practice of studios encoding discs this way has now stopped.
As already discussed DVD's have improved sound and picture capabilities, but they also have other benefits.
The following can be found on nearly every disc (so much so that we don't mention them in our disc reviews), although this is still up to the discretion of the manufacturer:
Not excited yet? Ok there are other options that can be included, however these features vary wildly from disc to disc:
There are many other features that are sometimes included, but these vary widely and there is not enough room to list them here. Of course some discs have few or no extra features.
This is the biggest single problem facing DVD, and it is all because of the greed of film studios. It works like this, the world is divided into a number of regions and films released in a region will only work on players of the same region. The reasoning behind this is supposedly to protect the staggered release dates of films in the cinema. However is more often used to fix prices within regions.
Not all DVD players have a fixed region. Many of the cheaper players are what is known a Multi-region. This means they can play DVDs of any region, just by inserting the disc. Other players have a fixed region code but by using a series of button presses the region can be altered, this is called Hacking. Some hacks require a different remote control to be used. It is worth noting that on certain models the region hack can only be used a fixed number of times before the last region becomes perminent.
So what happens if your player is not multi-region? Well it is possible to modify many players so that the region can be set automatically or manually, this is called chipping. This service is not offered by the major manufacturers, but by smaller third parties. Be warned unless the third party offers a guarantee this will invalidate your original guarantee.
You may be asking why should you bother. Discs of different regions vary both in availability and features. There are many films available for region 1 that have not been released in other regions. Lastly different cuts of the same film are sometimes available in different regions (due to the rules of local classification boards).
Is it legal to own or buy discs from another region, the answer in the UK is this. You may own or buy discs for personal use from any region. However it is illegal to sell discs from other regions in the UK. So to get your discs there are a few options;
Go to the region you want the discs from, or have a friend or relative who lives there send them to you.
Buy discs from a retailer in the region you require (using the phone or Internet).
NOTE: While both of these are legal and do work, you do run the risk of being charged import duty. The amount of this can vary, but it is sometimes waived.
The other option is to find a retailer that offers personal importation services (sometime they are based in Britain or outside of the UK, like the Channel islands).
Please note that while region 1s DVD will work in a multi-region player you will still a dual format television. This is a television that can recieve PAL (the UK tv format) and NTSC (the American television format).
As you can probably tell a lot of people own region free players (multi-region, hacked or chipped). This is much to the annoyment of the film studios, who are struggling to come to terms with the fact that the global economy is ruining their greedy plans. They still have one last trick up their sleves and that is Region coding enhanced. This is a modified version of the standard region coding test that has been included on certain region 1 discs. It works like this, firstly the player checks the region code as normal. If this check is passed it then checks to see if he player is capable of playing discs from any other region. If it can then the disc will refuse to play. As you can tell manually switched multi-region machines are unaffected by this. Auto switching region players may have problems, and some chipped players will require a new chip to defeat it.
It is possible to record to DVD in the same way it is possible to record to CD's using a special recorder and discs. It is still very much early days though and so early buyers should beware. The main problem is that their are currently three competing formats, and while they offer comparable performance they are all incompatible with each other (takes me back to the old days of VHS and Betamax, when will they learn).
Another current problem is the fact that they can only record on one layer of the disc, thus halving the capacity to about two hours. This will improve although the technology is still a way off.
The current recorders are expensive and what with the competing formats, and the fact that none of them may win (there are plenty of other digital recording devices not based on DVD technology on the horizon) it is best to wait and see.