Recording internal sound on a Mac is problematic as, unlike in Windows, you can't simply record whatever noise is playing. If you've ever got stuck wondering how to capture streaming audio from a website or any other sound playing through your Mac, here's how to do it:
2: Open System Preferences > Sound > Output. Now Soundflower is installed, you'll be able to choose it instead of the built-in output. Soundflower (2ch) is fine for most purposes. Note that once you do this you will no longer be able to hear sound. To make a clean recording, also turn off all sound effects here in the Sound preferences.
3: Open Audacity and in preferences, look under Devices and choose Soundflower (2ch) from the Recording Devices drop-down menu.
4: On the top right of the Audacity interface there is a microphone symbol with a drop down menu next to it. Click it, and hit 'Turn on monitoring'. You will now see red level indicators jumping whenever a sound is made. Play the sound or stream you want to capture, and adjust the microphone level-slider on the left so the red bars reach close to zero when they peak.
5: You're now ready to capture. Stop your stream, and pause it at the start. Hit the red record button in Audacity, then play your sound stream. Be aware that if you haven't turned off any sound alerts or effects, these will also be captured in your recording. Once finished, save the project from the File menu. At this point you can turn on the internal audio again in System Preferences. Any editing of your recording should be done now (See this post for audio editing with Audacity).
6: Again from the file menu, choose Export which allows you to convert your recording into a more useful format like MP3 or FLAC. You can now listen to your captured recording at your leisure.