Three Hollywood studios have thrown their considerable weight behind one of two competing formats for the next generation of DVDs, citing in part the need to stem piracy.

Paramount Home Entertainment, Universal Pictures and Warner Bros, which includes New Line Cinema and HBO, said yesterday they would start releasing films in the HD-DVD format by next Christmas.

The announcement escalates the battle between HD-DVD, developed by electronics makers Toshiba and NEC, and Blu-ray, backed by Sony, Matsushita Electric Industrial, which makes the Panasonic brand, and Philips.

The agreement is non-exclusive and the companies said they may produce DVDs in both formats if consumers demand it. But it also puts pressure on electronics makers to produce devices that support both formats. Privately, entertainment industry executives say they cannot afford a format war, reminiscent of VHS v Betamax in the early days of video.

While the Blu-ray format can store more digital programming than HD-DVD, proponents of the latter say it will be cheaper for manufacturers because it is uses technology that more closely resembles that used in current DVDs.

Blu-ray has the support of Columbia Pictures, which is owned by Sony, and Metro-Goldwyn-Mayer, which was recently bought by a group led by Sony. Other studios, including News Corp's 20th Century Fox and Disney, are still to decide on which format to support.

Both formats promise increased storage capacity and movie resolution superior enough to get the most out of high-definition TV sets. Both would also contain stronger anti-piracy protection.