• by Erik Sass , Staff Writer @eriksass1, March 13, 2013

The online audio scene is growing and changing at a positively maniacal rate, with several entirely new platforms in the works and countless new features from existing services. Frankly it’s all a bit overwhelming, but here’s my attempt at a brief roundup of this burgeoning, mutating marketplace. One thing is clear: Pandora should be very nervous.

Last year’s acquisition of We Are Hunted, an online music service, was a pretty clear signal that Twitter wanted in to the online music space, and that has now been confirmed, with CNET reporting that Twitter plans to unveil a music app, Twitter Music, as soon as the end of the month. According to CNET, Twitter Music will suggest artists and music based in part on who a user is following on Twitter, with an emphasis on music discovery. Songs will be streamed via SoundCloud, and you don’t have to have a Twitter account to use the service.

Meanwhile Google is also said to be planning a music service (or services) of its own, and has already struck a deal with Warner Music Group, as reported by Billboard last week. Google might operate several music platforms -- one affiliated with YouTube and another with Android via Google Play.

Then there’s Apple, which is planning its own ad-supported digital radio service, including customized listening and on-demand options. In addition to generating ad revenue, an Apple digital radio service could serve as a discovery mechanism that helps drive consumers to purchase songs outright via iTunes. According to the latest scuttlebutt , however, the new service has been delayed by stalled negotiations between the tech giant and various music labels; no surprise, the main sticking point is royalties.

And then there’s Spotify, which is said to be working on a new mobile streaming music service to compete with Pandora overseas, according to Bloomberg. The rumored service would combine Spotify’s on-demand feature, in the form of custom playlists, with music discovery through online channels based on listening preferences, akin to Pandora. A streaming mobile music service along these lines is already available to U.S. users.

Last but not least, Clear Channel’s iHeartRadio has unveiled “Add-Ins,” which allow users to short local news, weather and traffic updates into their custom stations. The Add-Ins draw localized, geotargeted content from Clear Channel’s network of 850 radio stations around the U.S.