I'm running OpenBSD -current on a 3rd gen Macbook, and have sound for the most part. However, I noticed that the headphones jack doesn't quite work properly.
If I plug in external speakers, with their own power supply, the audio over my built-in speakers lessens, but does not shut off. Also, zero sound comes out of the external speakers while this lessened sound continues out of the built-in speakers. Of course, I have not had this problem on other platforms. I have not even begun troubleshooting this. I have not tested to see if the same problem exists in -stable. I have not tried starting the system up with the headphones plugged in for proper identification of the hardware. This is being experienced on Intel HD Audio.
