There are a lot of solutions in Linux, under this U&L question. See details there, where also some solutions mentioned are cross-platform.
The general idea is that a YouTube track can be played as audio-only if:
- it is played in a video player with some 'no video' argument
- only the audio stream is sent to an external player
To send the YouTube track stream to the player the simplest way is probably SMTube - more here.
Open SMTube, search your title, right click on it, and select Open audio with:
Another cross-platform solution is to use Firefox with some add-ons: FlashGot or OpenWith.
See here how to use Firefox with FlashGot add-on or with OpenWith add-on in order to start YouTube (and other) videos in external players.
In FlashGot options the arguments can be added like here:
In OpenWith addon options, select Edit>Arguments, like here:
FlashGot add-on for Firefox can also select just the audio stream of the YouTube video as seen under the link above.
Selections look like so, after right-clicking the FlashGot icon that appears when playing the YouTube video in Firefox, and selecting 'Available formats'
then 'DASH (separate audio and video tracks)'
In this case, audio-only players can be used - some work and some don't (as far as I can tell testing in Linux, Audacious works). I will update this after testing more.
One of the best players to be used in this way is
mpv as video player.
mpv --no-video will start it without video, but also without any GUI or window: to enable window/GUI in all cases, add
profile=pseudo-gui in its config file, as indicated here; in Linux it's
~/.mpv/config, for Windows look here, or, just use another argument:
Example for Linux:
mpv --no-video --profile=pseudo-gui
To start VLC without video the commands are :
cvlc --vout none <URL>
cvlc --no-video <URL>
But from my experience
mpv works better that VLC for this purpose.
youtube-dlcan do this. Use the -F option to list available formats, and the -f option to select an audio-only format (e.g. 140 or 141). I'm not aware of any webapp which assists with this, or any way to get the youtube site to play audio-only.
youtube-dl -f 141 $URL. I would post this as an answer, but I can't do that because certain other muffin-heads posted bad answers so the question is locked down a bit. I'll go seek some reputation and come back later!