Dude, I understand you, how is it difficult to find a nice converter. On the market, there are a lot of free apps which are possible to use and on computers and even to convert Mp4 YouTube format to mp3 files. It is needed just to insert the link of needed video to
https://convert2mp3.cx/. It also has very fast conversion, don't see the reason why I should to wait for your app. I really appreciate this chance to hear podcasts and lectures in mp3 format for free during cleaning time, for instance. Can't imagine my life without it. Hope that I have helped you.