Use "find -exec" instead of "xargs"

If you need to run a command on each file under a directory structure, use the -exec option of find (it will substitute a file for each {}, and you must terminate with \;):

find some-dir -name '*.mp4' -exec ffmpeg -i {} out/{} \;

find ... -exec is better than piping to xargs because it handles filenames with spaces seamlessly.