How can I record the audio from my computer (Mac) ?

We don't have a built in way to do this on Mac (just windows vista or later).

Your best option is to install a 3rd party app called "SoundFlower"

This app will let you redirect the output normally heard on your speakers to a virtual microphone which you can then select as the mic to record in Screencast-O-Matic.

Feedback and Knowledge Base