I have a first gen Airport Express (from 2008) and use it with Mountain Lion. The connection chain looks as follows:
MacBook Pro -> WiFi (802.11n) -> Airport Express (receives Internet via DSL cable) -> Regular solid state amp
It works fine in the following situations:
- Quicktime video or audio
- Youtube using the HTML5 trial on Safari
- Vimeo on Safari
However, there's a huge sync difference (to be exact: 2 seconds) between audio and video when I use:
- Youtube, Vimeo (or any other video site) on Safari using anything but HTML5
- Youtube, Vimeo (or any other video site) on Firefox
A work around for VLC is to delay the video channel by 2 seconds to make the audio/video line-up again. But the browser is not as easily fixed.
From reading around on discussion forums this seems to be a Mountain Lion issue. Does Mavericks solve the audio/video sync problem when playing videos in Safari (or any other browser)?
For completeness I tried out the rather strange suggestion of Wheat Williams of connecting my MacBook Pro directly to the Airport Express using an Ethernet cable.
There was no difference at all compared to connecting through WiFi. The delay on VLC (if uncorrected) and on Firefox remained. This means that the connections speed is not the bottleneck.