I have installed the open-source BlackHole driver on macOS High Sierra and have set
BlackHole 16ch as both the Input Device and Output device (e.g. via Option+click on the volume icon in the Mac menu bar).
With this setup when launching QuickTime Player > File > New Screen Recording clicking the chevron now allows selecting BlackHole instead of the microphone, and the captured recording uses the better quality audio directly from the sound card rather than the microphone.
The problem is that while recording there is no real-time audio output via the speakers.
Tried adding a Multi-Output Device in the Audio MIDI Setup.app (it appears in Spotlight if you type "audio") and enabling both BlackHole and Built-in Output as shown in the screenshot below, and then selecting the Multi-Output Device as the Output Device in system sound settings (or via "Use this device for sound output" in Audio MIDI Setup), but then there is no sound from the speakers and the soundcard audio does not get recorded.
Is it possible to both record the sound card audio and output it in real time to the speakers?
NOTE: The audio I need to capture is not from the microphone but from an app.