YouTube Video to MP3 Conversion using website

I'm trying to make program that can download YouTube videos as mp3 files.

I used this site fbtube.biz in order to achive that.

So, i downloaded content of https://fbtube.biz/?c#?v=JePnQ1gSagc where JePnQ1gSagc is video id, now i have to get link to mp3 file(in this case https://fbtube.biz/get?video_id.....) but there is no link in downloaded content.

I noticed that chrome developers tools(ctrl+shift+j, tab Elements) show that link and view source(ctrl+u) option in chrome gives me the same result which i get by downloading page using java.

How can i get that link?