A key component to any digital audio service is the audio player--a software program used to play back digital audio, either as a stream or as a downloaded file. Depending on the type of audio service you provide, the decisions you will need to make about players will range from the simple to the fairly complex.
The developers of the common proprietary audio formats (Microsoft, Real, and Apple) provide players designed specifically to play back those audio files. While these players--like the audio formats--are proprietary, they are distributed free of charge to users in order to promote both the audio format and the player. In some cases, a basic, stripped-down version of the player is offered at no cost, and a ``premium'' version with added features is available for a charge. These features may include, for example, the ability to rip and burn compact discs.
Often the choice of player will depend on what type of audio files you plan to stream. Many of the proprietary players will not play sound files in formats supported by competitors. For example, Windows Media Player will not currently play protected AAC (iTunes) files, and the iTunes player will not currently play Windows Media Audio. If all of your digital audio is encoded in the same format, then it makes some sense to use the proprietary player associated with that format. On the other hand, if you offer audio in multiple formats, you must either provide multiple players or identify a single player that can handle all of the relevant formats.
For most libraries, there are two broad categories of listeners to digital audio services: those in-house who rely on library workstations for listening and those who use their own computers--either in-house or remotely--to access the service. The software requirements for the workstations used by these two categories of listener are different: an in-house listening station simply needs players that are compatible with whatever operating system and browser are used on public workstations. Often systems staff will include audio players as part of a standard public workstation ``disc image,'' and the only ongoing responsibility of the music librarian is to make sure the players continue to function whenever the browser software and the operating system are upgraded.
The situation is not so simple when providing service to remote users, who will prefer to access the service with their chosen operating system, browser, and audio player. In order to provide the best service to the largest number of users, you should run tests on computers running both Windows and MacOS to determine which software configurations are compatible with your service. (Linux users are used to being neglected and often derive some satisfaction from discovering workarounds on their own. And they'll tell you about them.) Of course, it would be impossible to test all permutations of operating systems, browsers, and players, but you should be able to recommend at least one successful combination of browser and player for both Windows and MacOS. Be sure to provide your users with a detailed list of systems requirements for your service--complete with web links to the pages where players and browsers can be downloaded--and update it regularly.