M4A and MP4 files

Support
1

When I encode wave using Nero, I get files with the extension M4A

Using Nencode, the file extension is MP4

Fundamentally, I dont understand this.
I become even more confused when attempting to Tag these files (MP3Tag with aac add on) as the Nero Files tag without difficulty but the nencode files wont with the message "No MPEG Header found in file" appearing.

I find this stuff rather confusing and as I am getting old (actually I am old!!) "please be gentle."

Thanks,
auldyin

EDIT
I know understand that M4A and MP4 are one in the same.
I have no idea about the tagging thing though

2

http://wiki.hydrogenaudio.org/index.php?title=AAC
http://wiki.hydrogenaudio.org/index.php?title=MP4

About nencode, I assume that it sets the wrong extension, if it produces a raw AAC file, the extension should be *.aac and not mp4 (but that's just a guess, I haven't used that program)

Mp3tag behaviour:
*.m4a *.mp4: file is assumed to be wrapped in a mp4 container, mp4 tagging is used
*.aac: file is assumed to be a raw AAC file without container, APEv2 tags are used