Looking at WindowsMediaFormat, it is always included on Windows, no matter what version and by the looks of it can always decode mp3s. On the Mac the CoreAudioFormat asks the system what formats it can decode and generates the format list at runtime, perhaps WindowsMediaFormat should do the same, I’m not sure but I guess its safe to assume its available and can decode the formats it returns.
If you’re not using an AudioFormatManager I highly recommend it, it takes care of all these issues and will give you a wildcard string for all decodable formats (so you can use it in file choosers etc.). My point was that maybe Jules should add the WindowsMediaFormat before his own to prefer this. Personally I build with MP3AudioFormat disabled to avoid any potential licensing issues but I haven’t benchmarked the two so don’t know if MP3AudioFormat is more efficient.