Originally Posted by rossmcm
The S4 seems to produce AMR files for "normal" quality voice recordings, and M4A files for "high" quality.
VLC media player can handle these files without complaint but I haven't yet successfully got iTunes or Windows Media Player to recognise them.
I thought I was able to do this with AMR files from another device by just renaming them but I haven't had any success with the S4.
I believe while ago QuickTime supported *.amr and it still does on my mac, but many users complain that they can no longer run these files. You should see if you can open them with QT and export to other, preferred format.
If no luck with that, you will need 3rd party tool, like:
Audacity: Free Audio Editor and Recorder