sclass DownloadAudio {

  S url;

  File dir = downloadedAudioDir();

  new LS options;

  S extension = ".mp3"; // used to have .opus but got bad quality sometimes

  int maxFileSizeInMB = 20;

  S cmd;

  *(WithURL<?> url) {

    this(url?.url());

  }

  *(S *url) {

    options.add("-U --no-playlist --no-mtime --write-description --write-info-json");

    options.add("--write-annotations --write-thumbnail --print-json --restrict-filenames";

    options.add("-x"); // audio only

    options.add("--audio-format " + dropDotPrefix(extension)); // demand our format

  }

  DownloadedMedia get() {

    if (empty(url)) null;

    installFFMPEGIfMissing();

    options.add("--max-filesize " + maxFileSizeInMB + "m");

    S fn = md5FileName(url);

    File infoFile = newFile(dir, fn + ".info");

    S json = loadTextFile(infoFile);

    if (isPossibleJSONMap(json)) {

      DownloadedMedia dm = new(null, json, extension);

      if (fileExists(dm!)) ret dm;

    }

    saveTextFile(newFile(dir, fn + ".url"), url);

    cmd = pqO(installYouTubeDL())

      + " " + joinWithSpace(options)

      + " -o " + pqO(newFile(dir, youTubeDLDefaultFileNameTemplate()))

      + " " + safePlatformQuote(url);

    S output = backtick_verbose(cmd);

    saveTextFile(infoFile, output);

    ret new DownloadedMedia(cmd, output, extension);

  }

}