A court in California will this month rule on the legality of an ingenious new software package that makes perfect copies of movies on DVDs even if they are protected with the latest anti-copying technology.

The software has been developed by 321 Studios of St Louis, Missouri. The company says its DVDXcopy program does not violate the 1998 Digital Millennium Copyright Act, which makes it illegal to defeat copy-protection schemes.

According to 321, the software is legitimate because it does not do anything that the DVD's copy protection is designed to prevent.

The movie on a DVD is stored as digital compressed code that is then scrambled using the industry's Content Scrambling System (CSS). Unscrambling is only possible on a DVD player or computer DVD drive that has CSS unscrambling keys stored in it.

The keys in the player mate with other keys buried in the DVD. Some of these buried keys cannot be copied even when a computer makes a bit-for-bit copy of the disc, so the copy will not play.

Perfect copy

As extra security the analogue TV signal that is fed to the TV screen is processed with the Macrovision analogue copy-protection system. So you cannot record that either.

Unauthorised software called DeCSS can defeat the CSS scrambler, and so-called "signal cleaners" can be bought to defeat Macrovision. But selling this software is illegal in most countries.

DVDXcopy works by intercepting the digital video code just after it has been legitimately unscrambled by the DVD player, but just before the unscrambled code is converted into a protected analogue TV signal. It then saves the unscrambled video on the PC's hard drive before copying it onto a blank DVD.

The copied discs play perfectly. It is even possible to copy the copy back to a hard drive, and then onto another blank DVD.

Part of 321's case is that its product reinstates the right of consumers to back up their discs. The argument dates back to the taping of records in the 1970s, but few in the entertainment industry accept its validity.

Burner factories

Earlier in 2002, 321 decided to assert what is sees as its right to sell its DVD back-up technology by suing nine major Hollywood studios, including Disney, Universal and Warner, when they complained about the capabilities of an earlier 321 technology, which copied a DVD movie onto several CDs.

Now 321 is asking the District Court in San Francisco to rule that selling its software to make back-up copies of DVDs does not violate the DCMA or any other US law. The case will be heard in mid-December.

The Motion Picture Association of America claims that piracy is costing studios $3 billion each year. It says it is already finding "burner factories" which illegally copy movies to blank DVDs.

The court case could go either way. "Copyright law says nothing about back-ups," says copyright lawyer Alistair Kelman. He says the key test is whether it is unfair to stop someone making a safety copy of something fragile. And the defence for selling software for copying is whether there is a legitimate use for it. "I can see judges jumping either way on this one," Kelman says.