Programming a
VST and
Au are actually pretty similar.
Before the invention of Core audio and
AU, Apple used to run plugs on VST2.
The coding underneath in either format is quite close, you just have to relate commands for CoreAudio and ASIO.
The real pain in the arse is the way that each platform handles there gui.
For that reason, I was told it's good advice to basically break the program in 1/2. I part audio process the other gui/front end code. It makes it a lot easier to port over later..
I've done a
VST (it didn't do anything fancy. It was just a gain) but not done an
AU. It's next on the list...