How to download playlist to mp3 format with youtube-dl?

I'm trying to download some videos in mp3 format. It's a playlist. How do I download the whole playlist using one command?

Both parts of this question (downloading in mp3 and downloading a playlist) are supported by youtube-dl:

youtube-dl --extract-audio --audio-format mp3 -o "%(title)s.%(ext)s" <url to playlist>

Some notes from me and the comments:

• Older versions of youtube-dl struggle with modern playlists. You might need to replace the repo version with the latest.

• cmo: You can ignore missing ("unavailable in your country", or removed) videos with an -i flag.

• frans: If your playlist isn't working and the URL contains a v=<ID> element, remove it so there's just the ?list=... item in the querystring.

Note:- Old version of youtube-dl is not able to download play-list. first you know what is your youtube-dl version. To check version of Youtube-dl use command

youtube-dl --version

version 2014.02.17 and older version not able to download play-list. If you use older version then update it by

sudo youtube-dl -U

after successful update use command

youtube-dl -cit https://www.youtube.com/playlist?list=PLttJ4RON7sleuL8wDpxbKHbSJ7BH4vvCk

Also you can create URL list in a simple text file and use following command.

 youtube-dl -cit -a file_name_in_which_you_paste_URL_list

For MP3 format Audio can saved. But audio saves as .m4a format on my machine.

youtube-dl -cit --extract-audio --audio-format mp3 https://www.youtube.com/playlist?list=PLttJ4RON7sleuL8wDpxbKHbSJ7BH4vvCk

NOTE :- If you install youtube-dl from Ubuntu software center. You can't update it from terminal.
Go Software center and update from it.
I test this commands on Wine because my youtube-dl also old. And I am unable to Update it.
If you can update your youtube-dl you can download play-list by using above commands.
I hope it helps...

There are a lot of instructions you can find using your favorite search engine. E.g.:

• www.xmodulu.com/...

For this Playlist it would be: youtube-dl -t https://www.youtube.com/playlist?list=PLYH8WvNV1YEnNVnJb5ZXxDCE2HDAVVo4M

I hope I could help you!

If you installed using pip, run the following to update:

 sudo pip install youtube-dl --upgrade

Enjoy...

an additon to Oli 's answer. If you have the playlist (in separate lines) with all URLs in it in a text file to download:

youtube-dl --extract-audio --audio-format mp3 --batch-file="/full/path/to/playlist"