Not supported anymore since iTunes 12.6 (March, 2017)
But it not only organizes and plays back audio. iTunes provides built-in visualization. By choosing “Show Visualizer” in the View menu, a visual show can be started that accompanies the music.
The menu item “Visualizer” lists all available visualizers as submenu items. The built-in “iTunes Visualizer” is always available, but other visualizers can be installed with ease as plug-ins.
On Mac OS X plug-ins are installed by placing the plug-in file inside the directory
Some visualizer plug-ins can be customized with a configuration window. The menu item “Options...”, that is displayed under the list of available visualizers, offers access to the configuration window of the currently selected visualizer.
While developing a custom visualizer plug-in for iTunes, I noticed that no comprehensive sample code with basic functionality existed.
The open source project is called “VizKit” . The first version was released in June 2004.
The iTunes visualizer “Cover Version” is based on the “VizKit” samplework.