If your music player supports OGG, you can also use youtube-dl -f FORMAT VIDEO_URL and give a numeric format that corresponds to a DASH webm audio-only stream, with vorbis audio (e.g. format 171 these days). The container is webm but it can be trivially changed to OGG with ffmpeg, which you can call via --exec automatically.

Edit: I mentioned that because you don't lose any quality reencoding.

That's my main use of youtube-dl for years now. I'm extracting audio from old french movies available on youtube, work a small sound extract with audacity and then post the result on soudcloud[1].

[1] A bit of self-promotion here, if you are interested this is my soundcloud playlist https://soundcloud.com/melicerte/sets/extraits-de-vieux-film...

I like to keep it in original audio format (usually AAC) instead of mp3, because with mp3 conversion, there is also some loss of quality due to re-compression.

Or you could use -x, which would only download the audio (because there's seperate audio and video streams on youtube).