Sometimes while I’m in the middle of a FaceTime call or during screen sharing the audio would suddenly cut off. The other party can hear me fine but I can no longer hear them. It appears that FaceTime always sends the audio to the Mac’s internal speakers, regardless of the system wide settings. Since macOS 11.4 it started doing this for calls routed via my iPhone too. All those calls are handled by FaceTime and the problem is caused by a long standing bug that Apple has not resolved yet.
The steps below help to get around the problem when it occurs. It is not a permanent solution though.
- Open the FaceTime app, even when you are in a call from the Contacts or screen sharing.
- In the Video menu select the correct input and output devices.
I set the input and output to the System default so that I can change it directly from the Sound icon in the menu bar. Hold the option-key before clicking to include the audio input choices.