`-o stdout' works with the default output format (wav)
and the normal redirection:

  csound -o stdout test.csd > test.wav

but it fails with the default and pipe (*nix OS)

  csound -f -o stdout test.csd | sox - -s -2 bounce.wav dither -s -f shibata

It is because

  http://www.mega-nerd.com/libsndfile/FAQ.html#Q017

It works in git, however you can use other output formats as `ircam'
and `au' (try to add `-J' in the previous example). Now, if libsndfile
fails with an output format and `-o stdout', it changes the format to
ircam and retries.

It is the same change that we have with

  csound -o '|sox - test.mp3' test.csd

Of course, there are not problems with stdin and pipe.

tito