I cant make anymore soundtracks until i find another app where a mp4 turns into a mp3

i make my soundtracks by starting with my screen recorder and making a random song (with a high pitched voice) then going to my app where a mp4 turns into a mp3 (Switch) and change the mp4 movie to a mp3 soundtrack then uploading the soundtrack

                       if you have anything you know about (exept for switch) please send me a link to its download