Audio Manipulation on Mac
loopback
If you wish to use an audio recorder to record audio being played by another application, such as capturing audio from youtube, you can use a loopback driver.
An Audio Loopback Driver is a virtual driver that allows one software to capture audio from another software. This is an alternative to capturing from a microphone. Simply holding a microphone up to your speaker would do a poor job of audio capture.
Example loopback virtual driver for MacOS