The Audio tab in the Publishing Settings dialog is for Opus Video Creator publications only. This allows you to set audio settings for the published video file.
Tick the Compress the SWF option if you want to compress the published SWF file – this option requires Adobe Flash Player version 6.
Make your changes to the other tabs in the Publish Settings dialog, then click the OK button to close the dialog and return to the third page of the Publish Wizard to start publishing.