Minor Description
We don't currently have mime magic detection for the Microsoft audio and video formats like ASF, WMV and WMA
From looking at http://file.fyicenter.com/File-Extension-WMA-Windows-Media-Audio.html the magic bytes for the ASF container format are 0x3026b275, and WMV and WMA are stored. From their sample files, we'd want to search for the unicode strings "Windows Media Audio" and "Windows Media Video" to detect within that.