how to donload a video form Youtube using ytdl-core in MP4 format

downloadVideoAsMp4.js

/**
  * Checks if the title is valid for being a file name, otherwise, removes the
  * characters that invalidates it.
  * A valid file name, is a string that does not contain any of the following:
  * / \ : * ? " < > |
  * @param {string} title
  * @return {string}
  * @private
  */
 validateFileName_(title) {
   return title.replace(/[/\:*?"<>|]]/, '');
 }
 /**
  * @param {string} userProvidedPath
  * @param {string} title
  * @private
  */
downloadVideoAsMp4_(userProvidedPath, title) {
    return new Promise((resolve, reject) => {
      const filename = this.validateFileName_(title);
      let fullPath = `${userProvidedPath}/${filename}.mp4`;

      // Create a reference to the stream of the video being downloaded.
      let videoObject = Ytdl(this.youtubeUrl_, {
	filter: 'audioonly',
	quality: 'highestaudio'
      });

      videoObject
	.on('progress', (chunkLength, downloaded, total) => {
	   //TODO: send event to UI to update progress
	});

      videoObject
	.pipe(fs.createWriteStream(fullPath))
	.on('finish', () => {
	  setTimeout(() => {
	    resolve({
		filePath: fullPath,
		folderPath: userProvidedPath,
		fileTitle: `${title}.mp3`,
	    });
	  }, 1000);
	});
    });
  }