AppleInsider correctly assumes that this feature likely refers to the local caching of the beginnings of songs, when the rest of the songs is located on a remote server. This would be a crucial aspect of any cloud-based version of iTunes, because it would allow songs in a music locker or subscription service to be downloaded to begin playing immediately — even when most of the data is streaming from a server somewhere (quite possibly in Santa Clara, California, from the look of things). That way, when a user presses play on a new song, or skips to the next song in an album or playlist, they can start listening immediately as the rest of the song downloads without encountering annoying lag time.

Apple’s patent application, however, covers something that both Pandora and Spotify have been doing for years: pre-buffering the beginnings of songs on a device’s or a computer’s memory, so they start playing immediately when the user skips to the next song. (Evolver.fm has asked both companies to comment on Apple’s patent, and will update this story if we hear back.)

When Evolver.fm asked Pandora founder Tim Westergren in Las Vegas earlier this year to explain how Pandora’s mobile apps manage to play the next song so quickly when a listener skips to the next song — even on relatively slow 3G cellular data connections while the user drives on a highway — he explained that Pandora always buffers the beginning of the following song, just in case you decide to skip to it.

Likewise, one reason Spotify users sing its praises is that it makes a remotely located catalog of millions of songs feel as if they all lived on your smartphone or computer. The way it does that — you guessed it — is by pre-buffering the next songs in a playlist or album, so listeners can skip between them without encountering noticeable delays. Spotify has been doing this since October 2008 — more than a year before Apple filed this patent application.

Caching is the secret to cloud based music — caching entire playlists for offline playback and caching the beginnings of songs the user is likely to play next. Only through that technique can cloud-based music feel “local,” as Pandora, Spotify, Slacker (and surely other cloud-based music services) have already figured out.

The one key difference in what Apple is doing here is asking the user whether to partially sync songs instead of just doing it automatically. Still, we have to ask. Can Apple patent something that these other companies are already doing? Stranger things have been known to happen.