SAN FRANCISCO  RealNetworks says it wants to help increase DVD sales by allowing people to copy their movie discs. Hollywood studios say that idea will only hurt their already struggling business. The two sides square off in a federal court here on Friday to determine who prevails.

The case is ostensibly about RealDVD, a $30 software program that allows users to save digital copies of Hollywood DVDs to their computers  a capability the movie industry strenuously objects to, worrying that it will stimulate piracy and undermine the budding market for digital downloads.

But the outcome of the trial, set against the backdrop of plummeting DVD sales, could also have more far-reaching effects on the future capabilities of the DVD player  a device connected to millions of television sets.

Before it started making RealDVD software for computers, Real was also developing DVD-saving software that it hoped to license to manufacturers of DVD players, according to the company’s executives and legal filings in the case.