Why M4a and not mp4?

[dinkypumpkin]

On 13/11/2012 23:27, Alastair wrote:
> I am advised that a file containing audio data only in AAC format can be named either .mp4
> or .m4a because it fits correctly into both the .mp4 and .m4a categories. Most servers,
> control points and music players understand this, but there are a few that insist on one of
> other of these filetype suffixes. In such cases it should be fine to simply rename the file
> from .m4a to .mp4 or vice versa.
>
> For a while now music and radio downloads have been put into M4a files and I think this
> may be upsetting some of my renderers.  I say think because I am still trying to sort out the
> tagging but meanwhile why M4a which I understand to be an apple format rather than mp4
> which is the ISO standard?  Is this an artifact from the BBC end or from get_iplayer.

Google would be your friend here. M4A and MP4 have the same container 
format.  The M4A extension is just a naming convention for audio-only 
files, a convention to which get_iplayer adheres.  For whatever reasons, 
some players won't recognise the M4A extension, so rename.