The codec-installer is not counted (put it int the engine-folder)
But the soundfiles are counted, and have to be in the game folder.

Any other custom dlls (like a render plugin etc) have to
be in the game folder.

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you should include the ogg-installer and the d3d - dll in the
engine folder, so someone without gamestudio has everything to install the
game without searching for these public files.

You could also make a "meta" installer, that sets up everything
automatically for convinience. But the 256kb game.zip must be manually openable.
(and dont let the installer "sneak" gamefiles into the
game)