Audio files

To minimise audio file (mp3):
ffmpeg -i name.mp3 -acodec libmp3lame -ac 2 -ab 64k -ar 44100 name.mp3

Remove All Metadata:
ffmpeg -i in.mp3 -map 0:a -codec:a copy -map_metadata -1 out.mp3

Remove Album Art:
ffmpeg -i in.mp3 -c:a copy -vn out.mp3

Convert mp3 to ogg:
ffmpeg -i input.mp3 -c:a libvorbis -q:a 4 output.ogg

-q:a 1-10 (higher number = higher quality)

Convert m4a to mp3:
ffmpeg -i filenameee.m4a -acodec libmp3lame -ab 256k output.mp3