flv2mp3.org is now known as flv2mp3.by and it's back to mp3 conversions
Youtube to mp3 – free, fast and easy-to-use
GitHub - appelblim/Flv2Mp3: A frontend for ffmpeg written in GTK+-3.0 / C capable of transcribing video files into mp3's of variable quality and setting metadata - this is very basic, it leaks
FLV2MP3 and 10 Best Alternative Sites to Convert YouTube to MP3 [Free]