The world's four biggest consumer electronics companies have agreed to start using a common method to protect digital music and video against piracy and illegal copying.

Japan's Sony Corp and Panasonic-brand owner Matsushita Electric Industrial, South Korea's Samsung Electronics and Dutch Philips Electronics said yesterday that they formed the alliance because they want buyers of their products to watch or listen to "appropriately licensed video and music on any device, independent of how they originally obtained that content," they said.

Such interoperability does not exist at the moment. Songs bought in Sony's Connect store on the internet, for example, can only be played on portable music players from Sony or companies that license its digital rights management (DRM) system.

Digital encoding and decoding formats also differ per store, with Apple using AAC in its iTunes Music Store and Microsoft using Windows Media. The lack of interoperability slows down the success of digital entertainment and the subsequent sales of devices, they feel.

The alliance, called the Marlin Joint Development Association (Marlin JDA), gives the companies standard specifications to build DRM functions into their devices that support commonly used modes of content distribution.Intertrust Technologies, a small United States-based company which owns many of the crucial patents for digital anti-piracy protection, is also part of the alliance.

The technology can be used in all products that get their content via the internet, broadcast or mobile phone networks.

A first version will come out by the summer, and it will support another, longer-term initiative, called Coral, which is aimed at developing a set of DRM-neutral agreements to ensure interoperability between all DRM systems and standards.