This article explains using youtube-dl to download a YouTube playlist using the best available audio format, and convert it to MP3 (using FFmpeg, which youtube-dl uses automatically for transcoding).
For this you'll need to have youtube-dl and ffmpeg installed on your system. youtube-dl stops working regularly due to changes to YouTube, so you'll want to have the latest version installed on your system. Since some Linux distributions tend to take a while until they update youtube-dl, I recommend removing the youtube-dl package installed from the repositories, and manually installing it as explained on the youtube-dl download page.
