This question has come up several times recently so I'm listing the FAQ that covers this issue here as well.
If you've recently updated to BrighAuthor 2.2 and you aren't getting any audio over HDMI, you need to update the audio output setting in BrightAuthor.
Under edit preferences, you can set the global default for audio output.
Also, in your currently project, under zone properties, you can set the audio output.See this articlefor more troubleshooting tips and a screenshot.
http://support.brightsign.biz/entries/168015-no-audio-but-video-plays-correctly