Piracy has already forced the music industry to adapt or face collapse - now it's the turn of the film industry. For every copy-protection system introduced, DVD pirates have found a way around it.
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By Paul Rubens
From military communications to remote car central locking, encryption is everywhere. It's also what makes the DVDs go around in your player, able to display a film in digital quality on a TV or computer screen.
Demand for DVDs is soaring
That's because ever since 1984 - when Sony won a landmark case which established video recorder owners' right to tape films broadcast on TV - studios have been horrified by the idea of consumers illegally making digital versions of their property.
Since DVDs contain digital copies of films, studios ensure that the discs are loaded with more copy protection systems than any other medium in history.
To prevent the data being copied, it's divided into blocks on the DVD. Each block is then encrypted using the content scrambling system, or CSS. The keys to decrypt each block are stored on a hidden area of the DVD, so copying a file to a computer or another disc leaves the keys behind. As a result, the film won't be playable.
Then there's regional playback control, which prevents DVDs bought in one part of the world being played in another - where the film may still be in cinemas.
DVD writers, which can be used to make copies of disks, are prevented from making copies of protected discs by another system, called CPRM.
Safe from harm?
All blank DVDs have a unique number called a media ID stamped on them, and if you copy a film onto one, it's encrypted in such a way that only this ID will decrypt the recording. But if you try to make a copy onto a new disc, it simply won't play because the new disc's ID is different - and so unable to decrypt the contents.
But what's to stop anyone from simply plugging a DVD player into a VCR or DVD recorder instead of a TV set, and pirating the film's analogue outputs signal as it plays? One final protection system - the macro-vision DVD copy protection system - interferes with this signal by adding pulses which confuse recorders and interrupt the picture, but which TV sets are immune from.
Pirated DVDs are said to cost the film industry $500m a year
With all this security in place, DVDs would seem to be safe from piracy. Not so. Today's cheap but powerful home computers make CSS laughably easy to overcome, and programs which break the CSS code in less than a second are available online.
Many, if not most, DVD recorders sold are "multi-region" - able to play discs from anywhere in the world - and CPRM can be overcome by decrypting a disc to a computer and then re-recording it.
The major obstacle to casual piracy turns out to be a simple practical problem. Many DVDs contain extra features, such as documentaries about the making of the film, and so are manufactured using dual-layer discs which can store almost eight gigabytes of data.
But DVD writers can only use single-layer discs, which have a capacity of less than 4.5 gigabytes. In order to fit the film on these lower capacity discs, pirates have to strip out the extra features that legal DVDs contain, or reduce the quality by compressing the data.
But now equipment manufacturers have announced that DVD writers and blank discs will be available within a few months which are capable of recording dual-layer DVDs.
Change and change again
So will DVD piracy kill the film industry? The music industry is adapting to the threat from pirated CDs by trying to introduce copy protection - a move which seems doomed to failure, given the ease with which DVD security has been overcome.
It's also developing new ways to sell songs, including by digital download with a rights management system - over the net. But while music lovers may download individual songs rather than albums online, there can be little attraction in downloading a small part of a film.
Piracy has also hit the music industry
And large scale downloading of entire movies is impossible in practice: the amount of data to be transferred is simply too big. Netflix, a DVD rental company in the United States, posts out hundreds of thousands of DVDs to customers every day, and the total amount of data these discs contain - about 5m gigabytes - is the equivalent of half the total traffic of the internet. The net is fine for delivering songs, but right now it simply cannot cope with everybody downloading films.
For the moment, the studios' eggs are all in the DVD basket, and it will be interesting to see whether an alternative can be found which isn't so easy to copy. Until then, movie moguls will have to accept that no encryption system will defeat a determined pirate, and rely instead on good old-fashioned honesty if the medium is to have a future.