I am not sure I understand what you mean. Word-splitting is performed by the "for x in y" construct, using the IFS variable, so by default if you have a file called "foo bar.mp4" the command line from the article:

  for i in *.mp4; do ffmpeg -i "$i" "${i%.mp4}.mp3"; done

will result in executing:

  ffmpeg -i foo foo.mp3
  ffmpeg -i bar.mp4 bar.mp3

Which is obviously not what was meant. So it's a good habit to learn to loop over files in a directory in a different way.

Maybe you are confusing this with what happens when you do

    for i in `find -name '*.mp4'`; do # ...

or similar. In that case, the output of `find` is indeed split first, and `for` sees "foo", "bar.mp4", and so on.

Ah yes, you are right, thanks!

Perhaps you have a very broken shell.

  $ function echon { echo $# $*; }                    
  $ >'foo bar.mp4'
  $ for i in *.mp4; do echon "$i" "${i%mp4}mp3"; done 
  2 foo bar.mp4 foo bar.mp3