Audible's .aa file format encapsulates sound encoded in either MP3 or the ACELP speech codec, but includes unauthorized-playback prevention by means of an Audible username and password, which can be used on up to four computers and three smartphones at a time. Licenses are available for schools and libraries.
Audible's content can only be played on selected mobile devices. Its software does enable users to burn a limited number of CDs for unrestricted playback, resulting in CDs that can be copied or converted to unrestricted digital audio formats.
Because of the CD issue, Audible's use of digital rights management on its .aa format has earned it criticism. While multiple software products are capable of removing the Audible DRM protection by re-encoding in other formats, Audible has been quick to threaten the software makers with lawsuits for discussing or promoting this ability, as happened with River Past Corp and GoldWave Inc. Responses have varied, with River Past removing the capability from their software, and GoldWave retaining the capability, but censoring discussions about the ability in its support forums. But there are still many other software tools from non-US countries which easily bypass the DRM control of Audible either with a sound recording or virtual CD burning method. After Apple's abandonment of most DRM measures, Amazon's downloads ceasing to use it, Audible's DRM system is one of the few remaining in place.
Many Audible listings displayed to non-U.S. customers contain the following text: "We are not authorized to sell this title to your geographic location." According to Audible, this is because the publisher who has provided the title does not have the rights to distribute the file in a given region. When a user is logged in, titles that he or she cannot purchase will be hidden.
There were hopes that Amazon, after its purchase of Audible, would remove the DRM from its audiobook selection, in keeping with the current trend in the industry. Nevertheless, Audible's products continue to have DRM, in keeping with Amazon's policy of DRM-protecting its Kindle e-books, which have DRM that allows for a finite, yet undisclosed number of downloads at the discretion of the publisher, however Audible titles that are DRM free can be copied to the Kindle and made functional.
Audible is able to offer DRM-free titles for content providers who wish to do so. FFmpeg 2.8.1+ is capable of playing Audible's .aa and .aax file formats natively.