M4A files (from YAMB) = slightly smaller filesize than original AACs?

[Christopher Woods (CustomMade)]

> *** Also is there anything technically incorrect about 
> creating audio-only MP4 files as opposed to M4A? ***
> 
> Hi
> Nothing 'technically incorrect' about it.
> The explanation is on Wikipedia.
> Here:- 
> http://en.wikipedia.org/wiki/Mp4#.MP4_versus_.M4A_filename_extensions
> 
> In Ubuntu all mp4 files are described as 'MPEG-4 video' in 
> the file explorer with an icon of a cine film.
> And m4a files are described as 'MPEG-4 audio' with a musical 
> symbol for the icon.

Interesting to know, cheers. I do remember when Apple started using M4A and
I went "...eh?" - I'm aware that M4A is loosely equal to MP4 (custom
metadata aside), but are there any particular internals arranged differently
or are there any small but crucial differences?

Also any insight as to why the wrapped AAC is smaller than the MP4? I'm
really quite curious about that.

Cheers :-)
Chris