Step 1:
When the video is done uploading, click on ‘file’ and then hover to ‘save movie’ and click on that. Now, keep scrolling downwards and you will find an option ‘audio only’. Click on that.
Step 2:
This will extract the audio and you can then give an apt name and choose the destination where to save it on your system.
Step 3:
Delete the video (if you only need the audio for it) and add as sound or music.
Source: Website