On a Mac:
Open the video file in Quicktime
Choose File
Click on Export As
Choose Audio Only
Pick your destination and save.
Done.
On a Windows computer:
(Or a Mac), unfortunately they seem to need additional software for this.
Download VLC (free and pretty much standard) at https://www.videolan.org/
Open VLC
Choose Media (or File)
Choose Convert / Save
Click browse and choose your file, or drag and drop your video file.
Choose the profile “mp3”
Choose your destination and save.
Online tool for extracting sound from a video file:
There are a few free tools to do this, here we’re using: https://audio-extractor.net
Upload your video file, wait for it to complete.
Select “mp3" as format.
Click “Extract audio”.
Confirm the download in the next step by clicking “Download”.
Done.
Want to use this file to create an SRT file? Read more here.