Earlier today Apple released iTunes 12.1, which brings a few fixes for some known stability issues, and also improves syncing with various iOS devices. In addition, Apple has included a Notification Center widget that will allow you to control iTunes from the Notification Center sidebar. This option gives you similar convenience to Apple’s iTunes Dashboard widget, and adds to the numerous options Apple already includes for controlling iTunes from small window. However, upon installing iTunes 12.1 you might not see the widget available right away.
To get the widget working, you might first have to enable it, which can be done in the Extensions system preferences, where all of your Notification Center widgets and other extensions for programs are managed. In this system preferences pane, simply check the iTunes widget, and then optionally drag it up or down in the list to change its position in Notification Center.
For now, these features seem to be the extent of the new widget’s functionality, though Apple could update it with new tweaks as new versions of iTunes are released.