Ubuntu Mac Mini and Retropie HDMI sound problem FIXED
I've installed Ubuntu and Retropie on my Mid 2010 Mac Mini, it's running a 2.4Ghz Core 2 Duo with a Nvidia Geforce 320M graphics chipset. Everything including N64 titles run great, but couldn't get the sound to play through the HDMI output to the TV.
Seems to be an issue with Ubuntu, Mac-Mini's and Nvidia Chipsets.
I finally found a post that suggested updating the Nvidia drivers with the following commands in terminal.
sudo add-apt-repository ppa:ubuntu-x-swat/x-updates
sudo apt-get update
sudo apt-get install nvidia-current
I rebooted and my sound started working
Hope this helps anyone having a similar issue.