Convert Audio files online with! enables users to convert audio files to and from popular audio formats (MP3, OGG Vorbis, Flac, WMA, M4A, Wav) on-the-fly. The website feature a simple interface to accept input file and to provide feedback once the file has been converted.

Ogg Convert Logo

Best of all, it does not require registration!

How to extract Audio from Youtube Flash Video (FLV) in Ubuntu Linux

First you need youtube-dl tool or ‘cclive’ to download the Youtube .FLV file.

Then, download the Youtube stream.
python youtube-dl

Alternatively, you can use ‘cclive’ to download the youtube stream.

After that, use ffmpeg to extract the audio and encode it to MP3
ffmpeg -i lee7a55401e.flv vn -acodec libmp3lame -ab 128000 -ar 44100 lee7a55401e.mp3

Note: You need to install the restricted codecs in order to extract MP3 audio files.

Thanks Mohammad Bahathir Hashim for the tip!