Hi

Where can I get such a command line tool from? So I can encode and decode AMR audio files.

I was searching for this kind of tool when I got a T630 cellphone with AMR support a few years ago and I didn't find anything suitable. Finally, I made this simple thing - it works quite well, but:
1/ it just uses a converting library "amrconverter.dll" from something called "Sony Ericsson MMS Editor" (at least that's what I wrote there back then). I'm not sure of the licensing of it, so I better won't give a public download link, but I can send it privately if you won't be able to find it anywhere else.
2/ the library is awfuly written, weirdly slow, it creates temporary raw files, etc.
But definitely still better than nothing, it did the job for me flawlessly.

Sounds interesting. Does it have stdin and stdout functionality?
Could you PM me the dll?

Thanks for the info!

No, because of the fact that the library interface is only on filename level.
(More in the PM.)

There are tons of different variations of AMR as source code at http://www.3gpp.org/ftp/Specs/html-info/26-series.htm