Windows Media Player (abbreviated WMP) is a proprietary digital media player and media library application developed by Microsoft that is used for playing audio, video and viewing images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices. Editions of Windows Media Player were also released for Mac OS, Mac OS X and Solaris but development of these has since been discontinued.
Compared with its versatility on Microsoft PC, WMA shows its shortage on Apple products including Mac computer, iPod, iPhone and iPad. Generally speaking, Apple doesn't allow people to import WMA, and the most common audio format on iPod and iPhone is MP3 or AAC.
How to get this trouble fixed out? Audio Converter Plus comes up, which allows you to convert WMA files to M4A, MP3, etc.