sclass JVideoLibDownloader is Swingable {

  transient SingleComponentPanel scp;

  selfType forward(IF0<JComponent> forward) {

    this.forward = forward;

    this;

  }

  swappable JComponent forward() {

    ret jcenteredlabel("Video extensions enabled");

  }

  S libID() {

    ret ffmpegLibraryIDForPlatform();

  }

  bool videoSupported() { ret libID() != null; }

  bool libDownloaded() {

    ret fileExists(DiskSnippetCache_getLibrary(libID()));

  }

  bool hasLib() {

    bool has = currentProgramHasLibrary(DiskSnippetCache_getLibrary(libID()));

    print("Video library ID: " + libID() + ", loaded: " + has);

    ret has;

  }

  void addLib() {

    if (videoSupported())

      if (addLibraryToCurrentProgram(libID()))

        print("Video library loaded: " + libID());

  }

  visualize {

    if (scp == null)

      scp = singleComponentPanel(makeComponent());

    ret scp;

  }

  JComponent makeComponent() {

    if (!videoSupported())

      ret jcenteredlabel("Video playback is not yet supported on your platform");

    if (libDownloaded()) {

      addLib();

      ret forward();

    } else

      ret jfullcenter(centerAndEastWithMargin(

        jcenteredlabel("Download video player for " + platformName() + "(ca. 20 MB)?"),

        jbuttonWithDisable("OK", r addLibWithProgressBar)));

  }

  void addLibWithProgressBar {

    scp.setComponent(jcenteredlabel("Downloading extension..."));

    try {

      addLib();

      scp.setComponent(forward());

    } catch print e {

      scp.setComponent(jErrorView(e));

    }

  }

}