More and more libraries are offering downloads of audio book files to their patrons, but the prevalence of the Windows Media Player format means that iPod owners can’t take the materials with them.

Michael Hill, writing for the Associated Press, notes: "Vendors such as OverDrive Inc. and OCLC Online Computer Library Center Inc.’s NetLibrary have licensing deals with publishers and provide digital books using Microsoft Corp.’s Windows Media Audio format, which includes copyright protections designed to help audiobooks stand apart from the often lawless world of song swapping."

When an audio book file is due to be "returned" to the library, the patron must renew it or find that the accompanying encryption has rendered it useless, Mr. Hill explains. He talked to OverDrive CEO Steve Potash, who said that he has around 1,000 libraries signed up for his company’s service. NetLibrary has 200 libraries using its audio book services.

To get around the compatibility problem, users can burn the audio book files to a CD and then import those into iTunes, an option that OverDrive offers but NetLibrary doesn’t. Mr. Hill was able to reach an Apple spokeswoman for his story, but she wouldn’t comment on the incompatibility issue and only said that the company "has no plans to change its copy-protection formats."

According to Mr. Hill, one library has avoided the download services because of the iPod problem. He writes: "Newport Beach Public Library bought 15 iPod Shuffles and loaded them up with audiobooks from iTunes to loan out. Patrons are liable for any loss or damage, though librarian Genesis Hansen said there’s been no problems so far."