I'm not sure, if it is possible to do that directly in Mathematica, but there is a command line tool called youtube-dl. It allows the direct extraction of the audio by using the -x option, see here Post-processing Options.

Example:

youtube-dl https://www.youtube.com/watch?v=jNQXAC9IVRw -x --audio-format mp3

You can use Run[] to run the command directly from Mathematica.

I'm not sure, if it is possible to do that directly in Mathematica, but there is a command line tool called youtube-dl. It allows the direct extraction of the audio by using the -x option, see here Post-processing Options.

Example:

youtube-dl https://www.youtube.com/watch?v=jNQXAC9IVRw -x --audio-format mp3 -o "only_audio.%(ext)s"

The audio will be saved in a file called only_audio.mp3.

You can use Run[] to run the command directly from Mathematica.