Keeps aspect ratio
find . -iname '*.png' -exec convert \{} -verbose -set filename:base "%[basename]" -resize 64x64 "./64x64/%[filename:base].png" \;``
Forces size:
find . -iname '*.png' -exec convert \{} -verbose -set filename:base "%[basename]" -resize "64x64!" "./64x64/%[filename:base].png" \;``
Audio, reduce/increase volume
ffmpeg -i input.wav -filter:a "volume=0.5" output.wav
Ref:
https://askubuntu.com/posts/135489/revisions
https://trac.ffmpeg.org/wiki/AudioVolume