The information in this article applies only to:
Microsoft Windows Media Player for Windows XP
Windows Media Player for Windows XP has MP3 encoding plug-in support. To enable the Windows Media Player to encode MP3 files, you must download and install a compatible MP3 encoder. Windows Media Player supports only Audio Compression Manager (ACM) functions to communicate with the MP3 encoders. Therefore, the codec must be an ACM codec. I use the Fraunhaufer Pro ACM MP3 Codec. you can get it, like all other files, from my site.
MP3 Compression Only. Windows Media Player for Windows XP supports only plugging in an MP3 encoder. Using any other compression creates invalid MP3 files. Therefore, the only compression support that is provided by the codec is for MP3. The codec accept only raw data and output-compressed data.