If you don’t want to install Apowersoft_AudioDevice (Apowersoft Virtual Sound Card) or the installation failed, you can try to enable Stereo Mix to record system sound (What U Hear).
In fact, recording whatever is being output is easy. The only hang-up is accessing that recording channel, which can be done rather easily. You can follow steps below to solve the sound recording issue.
After you’ve installed Soundflower, launch the Sound system preference and you’ll see Soundflower in the Output and Input tabs. Select the Output tab and choose Soundflower (2ch).
When you choose Soundflower as your Mac’s audio output, you can no longer hear it through attached speakers or headphones. In order to monitor what’s happening, launch the Soundflowerbed application (found in /Applications/Soundflower). Click the Soundflowerbed menu bar item that appears and choose your speakers or headphones from the menu. Now, the audio application can capture what is being played on your Mac, and you can listen to the source audio as well.
To configure Mac Screen Recorder, just choose Options -> Recording -> Audio. In the Microphone device, select the Soundflower (2ch), and then return the the main interface. Next, click Audio Input menu, select Microphone as the input audio source.
Start recording, I think you will record the system sound now.