I have a Cinema Display attached to my MacBook Pro via DisplayLink/Thunderbolt. If I also have a headphone cable plugged into my MacBook Pro, all audio output gets routed to the headphones. If I try to select "Display Audio" as my output destination, it just reverts to "Built-in Output".
This is different from the known issue with not being able to enable built-in audio when the headphones are plugged in; the speakers on the display are shown as a different output target in Audio MIDI Setup.
All I want is for sound to be sent to the display if it's attached and otherwise do the normal thing. It feels like this is what the Mac is trying to do, except for the headphones thing.
I can use Soundflower to redirect my output to one or the other, but I can't figure out a way to automate that task, plus Soundflowerbed seems to crash every time Display Audio appears or disappears.
I can set up a Multi-Output Device with "Built-in Output" and "Display Audio", and select it as my output target, but then I lose the ability to control volume in any useful way: the volume controls don't do anything but pop up a grayed-out speaker icon with a slashed circle.
I can use Soundflower as my default audio target and have it redirect to the Multi-Output device, and that comes really close, as I can then control the volume of Soundflower in the normal manner, but it seems to cause some reasonably significant audio degradation, and it seems to cause Soundflower to occasionally produce what sounds like about a 150Hz buzz at top volume that is unresponsive to anything other than changing the output target, which isn't the quickest thing to get to.
This is under MacOS 10.7.4.