Apple Computer is coming under pressure from some of Hollywood’s biggest movie studios to change the operating environment of its popular iTunes platform, amid growing concern about digital piracy.

The studios – Universal, 20th Century Fox, Paramount and Warner Bros – are in talks with Apple about making their films available for digital download on iTunes.

After months of discussion, a sticking point has emerged over the studios’ demand that Apple limit the number of devices that can use a film downloaded from iTunes.

The studios want to avoid the experience of the music industry, which has yet to recover from years of illegal digital piracy. Apple must introduce a “new model” for feature film content delivery, said one studio executive involved in the talks.

With the average cost of a blockbuster film approaching $100m, movie studios had more to lose than music companies, he added. “We’re very willing to do a deal but we’re keen to get some concessions from Apple that will account for the differences between the value of music and television content and feature film content.”

The talks between Apple and the studios come as retailers are scrambling to get to grips with digital delivery of film content. Wal-Mart, the largest US retailer, is entering the nascent market, challenging Amazon and Apple with a different model that ties digital downloads to the sale of DVDs.

Customers buying the newly released DVD of Warner Bros’ Superman Returns, will be able to download a digital version of the film on to a portable device, a personal computer, or both for a small extra payment.