Warner, Paramount, Universal and New Line Cinema have all agreed to issue movies in the upcoming HD DVD format, the disc's co-creator, Toshiba, said today.

The four represent 45 per cent of the major studios' DVD output in the US, the Japanese giant said.

Pre-recorded HD DVDs are at least a year away, but with Sony aggressively pushing its rival high-capacity optical disc format, Blu-ray, Toshiba clearly feels it has to follow suit.

Both technologies boost the capacity of the 12cm disc by using a blue laser to read the data off the carrier rather than the red laser today's DVD systems use. Blue light's shorter wavelength means that the 'spots' on the disc's surface used to encode digital data can be smaller. In turn, smaller spots means more of them in a given area - a higher capacity, in other words.

Blu-ray wins on the capacity front, offering 25GB on a single-layer disc to HD DVD's 20GB and a more aggressive roadmap to increase that capacity over time. The downside is the need for entirely new disc production lines. HD DVD, by contrast, only needs existing DVD pressing rigs to be retooled rather than replaced. It also has the strength of the DVD brand, which has been very strongly pushed to consumers over the last seven years or so.

And now the format has clear studio backing. But so does Blu-ray, with Sony almost certainly offering content on the medium, and possibly MGM - recently acquired by Sony - and 20th Century Fox, too. ®

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