Sound and the microphone on Mac boxes

A macOS box on Tart can hear and play sound, so a test can speak to an app and record what it plays. Nobody has to approve anything first.

The microphone

The box’s default input is BlackHole 2ch, a virtual audio device. What is played to its output comes back as the microphone. To feed speech to an app in the box, run:

say -a BlackHole "Hello from the test"

The app listening on the default input hears it. A VM that can be suspended has no audio input device of its own, so BlackHole is its microphone.

Apps an agent starts

An app that box_run starts in the desktop session (desktop: true) has the microphone, the camera and the system’s audio without a prompt. bb-box’s launcher starts it, and macOS treats the launcher as the app’s responsible process, as it treats Terminal for what Terminal starts.

An app opened with open -a is its own responsible process, so macOS asks about it. Computer use can answer the prompt.

Where this comes from

The macOS image sets this up when it is made. See the Tart setup guide.

On a Mac of the SSH host pool

A Mac of the SSH host pool has BlackHole 2ch as its input too: its setup installs it, and say -a BlackHole feeds it speech in the same way. On a Mac with System Integrity Protection off, a command box_run runs has the microphone and the camera with no prompt. A program started as its own responsible process, such as an app opened with open, needs box_grant for them, and box_grant’s system-audio to record the system’s audio. The Mac has a camera only if one is attached, such as a USB webcam.