If you want to record audio from your computer outside of Ableton Live such as capturing audio from your favorite viral video, here’s how.
On Mac, download and install soundflower.
IF INSTALLING ON Mac OS HIGH SIERRA
The first attempt to install will display a security alert, then fail. Afterwards, you need to go into System Preferences “Security & Privacy – General” pane and give permission to allow the install signed by the developer “MATT INGALLS”. After giving permission, you will be able to run the installer successfully.
Then change your Mac system preferences audio to route out to soundflower 2ch. In Ableton Live, change your input to soundflower 2ch, but keep your output in ableton still set to your soundcard or interface output.
If you arm an audio track with the audio from on Ext In and change the input to 1/2, you should now be able to hear and record your computer’s audio from videos and other sources running through Ableton. Make sure to set the track Monitor to “Auto.”