Codec for .m4a files by ds | May 13, 2012 | Software | 0 comments This entry has been published on 2012-05-13 and may be out of date.Last Updated on 2012-05-13. Windows Media Player does not play .m4a files by default. You can either convert them to mp3, or use this codec. It’s free, easy to install and works under XP, Vista and 7. Submit a Comment Cancel replyYou must be logged in to post a comment.