YouTubeDl('http://www.youtube.com/watch?v=' + videoId, {
            filter: function(format) {

                return format.container === 'mp4';
              }
            })
            .pipe(fs.createWriteStream('music.mp3'))
            .on('error', function(err) {

              //Do smth. with error
            })
            .on('finish', function() {

              //do smth. on finish..
            });