M4A = technology from MPEG4. Motion Picture Expert Group Layer 4 Audio. It's truncated to 3 letters because of the limits of 8dot3 format. All files had to fit into this. Since Windows95, files have been able to use LFN support - Long File Name so the 8dot3 format can be broken.
The easiest and failsafe way I do it when I want to be lazy is to burn to disc and rip from it as MP3 when I can't be bothered to convert it to MP3 directly. There are audio converters out there, but a lot of sound files need decoders. The term CoDec is usually required to convert into a format. Converting to MP3 would require the coder to encode. Reading from would require the decoder, hence Windows Media Player has the MP3 codec as standard from version 10, so you can rip to MP3 instead of WMA