sclass JVideoLibDownloader is Swingable {
  transient SingleComponentPanel scp = singleComponentPanel();
  
  S libID() {
    ret ffmpegLibraryIDForPlatform();
  }
  
  bool videoSupported() { ret libID() != null; }
  
  bool libDownloaded() {
    ret fileExists(DiskSnippetCache_getLibrary(libID()));
  }
  
  bool hasLib() {
    ret currentProgramHasLibrary(libID());
  }
  
  void addLib() {
    if (videoSupported())
      addLibraryToCurrentProgram(libID());
  }
  
  swappable JComponent forward() {
    ret jcenteredlabel("Video extensions enabled");
  }
  
  visualize {
    scp.setComponent(makeComponent());
    ret scp;
  }
  
  JComponent makeComponent() {
    if (!videoSupported())
      ret jcenteredlabel("Video playback is not yet supported on your platform");
    else {
      if (libDownloaded()) {
        addLib();
        ret forward();
      } else
        ret jfullcenter(centerAndEastWithMargin(
          jcenteredlabel("Download video player (ca. 20 MB)?"),
          btnOK = jbuttonWithDisable("OK", r addLibWithProgressBar)));
  }
  
  void addLibWithProgressBar {
    scp.setComponent(jcenteredlabel("Downloading extension..."));
    try {
      addLib();
      scp.setComponent(forward());
    } catch print e {
      scp.setComponent(jErrorView(e));
    }
  }
}