Streaming audio between two Macs

Macs can share video, so that you can use a Mac from a remote Mac, as if you were sitting in front of it. The Share Screen feature makes remote access to another computer incredibly easy. You can use a Mac’s display, keyboard, mouse or trackpad from the controlled Mac. You can even access all the peripherals connected to that other Mac.

But you can’t hear the sound from it. Audio is not shared. A commercial solution to this missing feature is Rogue Amoeba’s Airfoil. A free one, that you might already have in your computers, is Skype, together with Soundflower or Rogue Amoeba’s Loopback.

First of all, install Soundflower in your controlled Mac. You can download it for free from the developer’s site (Matt Ingalls). Once it is installed in your Mac, you get a virtual audio stream between applications. An application sending audio via Soundflower can be recorded by an application that has Soundflower as its audio input. It is like a virtual cable running between applications.

In the controlled Mac’s System Preferences > Audio control panel, choose Soundflower (2ch) as the audio output. You can do the same from the audio icon on the right side of the Mac menu, if you have checked the relevant option. At this point, the Mac is outputting stereo audio via Soundflower.

Then, go to Skype’s Audio and Video settings, and choose Soundflower (2ch) as the audio input device. This makes Skype listen audio from Soundflower, instead of the microphone. Any application sending audio to the Mac’s audio output (that is now Soundflower) will send audio to Skype.

From the controlling Mac, log into Skype with a different account. Call the local Mac from the other Mac. When you answer your own call, you can listen on the controlling Mac the audio generated by the controlled Mac.

Please keep in mind that, depending on the speed of the connection, audio may be delayed. Skype should choose to connect via the LAN, and not via the internet, but its audio stream will not be in realtime. Lip-synching, for example, may not be perfect. However, this should be enough to prelisten to a score or an edited sound.