Error message....

Hello, I have installed MOC 2.6-alpha3 and moc-ffmpeg-plugin.
I can listen to files of MP3, however when I attempt to play files of M4a, I get an error saying something like this:
Can't get decoder for exsmple.m4a

Dose anybody have any experience or any idea for this problem.

You need to supply more information. At the very least, your distro. It looks like `ffmpeg` decoder was not found. Checking MOC log would provide more information (either `mocp -D` or if you don't have a debug-enabled version, `mocp -SF` to start server in the foreground).