This is a serious problem for most people trying to record their screens since it is impossible to make engaging content without any audio. QuickTime doesn't capture audio playing on your Macbook's internal audio card: for example, it won't record the sound coming from programs like games or music interfaces. However, QuickTime comes with a set of challenges, the most severe being that it doesn't capture internal audio. It's common knowledge that Apple offers a built-in screen recorder, QuickTime Player.
Differences Between Internal Audio and External Audio