Windows Media Audio (WMA) is an audio data compression technology developed by Microsoft. The name can be used to refer to its audio file format is audio codecs. It is a proprietary technology that forms part of the Windows Media framework. WMA consists of four distinct codecs. The original WMA codec, known simply as WMA, was conceived as a competitor to the popular MP3 and RealAudio codecs. WMA Pro, a newer and more advanced codec, supports multichannel and high resolution audio. A lossless codec, WMA Lossless, compressed audio data without loss of audio fidelity (the regular WMA format is lossy). WMA Voice, targeted at voice content, applies compression using a range of low bit rates.
The M4R file type is primarily associated with 'iPhone' by Apple Inc.. This is basically a renamed AAC (M4A) file.