AT&T has launched an aggressive campaign to convince others, including Apple, to license its MPEG video compression patents.

The company claims several patents that relate to video compression within the MPEG-4 standard. To make its claims it has begun campaigning to make Apple, CyberLink, DivX, InterVideo and Sonic Solutions agree to licences.

However, representatives from the companies named don't believe they need to take out a licence, reports PC Mag.

As part of its campaign, AT&T is contacting US retailers that distribute products from the companies, warning them that by stocking those goods they too could be held liable for patent infringement.

It claims to be offering licences under reasonable terms, warning retailers that they are responsible for ensuring the products they stock are licensed. In cases such as hardware and software with support for MPEG-4 from Apple, retailers must get a licence themselves if Apple doesn't.

AT&T warns it will pursue damages and legal costs.