Converting streaming video links to audio files in one step

[Nollaig]

I was streaming a Youtube video via VLC yesterday and heard a song being used as background music that I quite liked the sound of. Unfortunately the uploader had given no details of the music used in the video, so I decided to go and find out myself. I wanted to use one of those sites where you upload a mp3 file of the song and it identifies it for you, so I went to download the stream as a video file via VLC, and then convert it to an mp3 file in the usual way.

As I reopened the stream in VLC to do this, I noticed that in the "Open Media" dialogue box, under the "Network", instead of clicking on "Play" you could also choose from "Enqueue", "Stream", and most interestingly "Convert". Clicking on Convert, it brought me to the usual file type conversion window, and I assumed that this would allow me to bypass the step of downloading the video and instead download directly in mp3 format. However, once I set it up to do this and started the download/conversion process, VLC player minimized and I did indeed get a mp3 file in the destination folder - but it contained no data.

Has anybody any idea what I might be doing wrong? Or is there perhaps an alternate way to achieve what I'm trying to do on VLC player?