How to use the ytdl-core.filterFormats function in ytdl-core

ytdl.getInfo(youtubeMetadata.link, infoOptions, function(err, info) {
      if (err) {
        log.error('YTDownload', JSON.stringify(err));
        reject(err.message);
      }

      var downloadOptions = {
        quality: 'highestaudio',
        requestOptions: { maxRedirects: 5 },
        format: ytdl.filterFormats(info.formats, 'audioonly')[0]
      }

      // Setup stream
      var stream = ytdl.downloadFromInfo(info, downloadOptions);
      stream.on("response", function(httpResponse) {

        // TODO: Add event emitter to share progress with caller

        // Build progress var
        var str = progress({
          length: parseInt(httpResponse.headers["content-length"], 10),
          time: 1000
        });

        // Stream progress listener
        str.on("progress", function(progress) {