Linux.com is running a very informative article on Phonon, the new multimedia layer for KDE 4. It explains the rise and fall of Phonon's predecessor aRts and elaborates on the ups and downs of an audio abstraction layer. The article also gives an overview of common use cases and provides some example code. The Phonon website itself provides more code examples and documentation for using the Phonon API and for writing a backend. In addition to the existing NMM backend by Bernhard Fuchshumer, Tim Beaulen is working on a Xine backend for Phonon.