Audacity 1.3.6 Beta adds support for editing WMA, M4A audio files
Here's how to set it up. First you need to install Audacity 1.3.6 beta, and then find the preferences menu under the edit tab. Next, click the Import / Export option. If you already have FFmpeg on your system, click the find library button and locate the avformat-52.dll file. If you don't have FFmpeg yet, click the download button and a web browser window will open up with instructions for downloading and using the plugin.
The latest version of Audacity also has a few other tweaks, like improved performance when laoding uncompressed audio files and the ability to link audio and lable tracks so that labels move properly when you move an audio track.
[via Making Music]