m4a Format
 

I have a set of m4a files. They play fine in iTools and also in RealPlayer ... but not in WinAmp. Why?

Good question.

We will need a sample file to be able to help you any further.
Upload one to sendspace.com and post the link here.

If the files are encoded with Apple Lossless codec, then you will need to install the ALAC Decoder for Winamp 5.32, which comes with the Essentials Pack
(see Winamp 5.32 Released thread for details/download).

And that's assuming you're using Winamp 5.32, and the Nullsoft MPEG4 Audio Decoder plugin (in_mp4.dll), which comes with the Full, bundle and Pro packages (ie. not Lite) is installed...? (ie. including a List of Plugins might also help us to help you).

Thanks, that was probabaly the reason. Unfortunately I can no longer verify the situation because I used iTools to cut the CD and then removed the files.