Hi folks

If you have either a Linux system or a Windows system with BASH installed on it then the job is simply done with the following script.

for f in *.m4a; do ffmpeg -i "$f" -c:a flac "${f%.m4a}.flac"; done

For Ubuntu users - (physical or VM's) you might get a message saying ffmpeg is deprecated --that's not actually true --just download the current version.

Some music apps on phones won't always play m4a files but they all will generally play FLAC - and with decent capacity micro sdhc cards and a proper set of headphones there's no reason to have horribly compressed mp3 music -- I'd recommend if you must use mp3 stick to 320 kbs or at the very least 256 kbs.

The DACS in most decent smart phones are perfectly good to give a good rendering of uncompressed music -- and decent headphones such as BOSE / Sennheiser etc even on blue tooth will be more than satisfactory.

BTW if you can still find a copy of Winamp on Android it will actually play mp4a (always assuming the smartphones hardware can handle it).

I'm still using good old winamp pro on my Windows system --still works even on Windows 10 !!.