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public void DisplayPlaylist(Playlist playlist)
{
    Thread thread = new Thread(() => DisplayElements(playlist));
    thread.Start();
}

private void DisplayElements(Playlist playlist)
{
    for (int i = 0; i < playlist.elements.Count; i++)
        DisplayElement(playlist.elements[i], i);
}

private void DisplayElement(IPlayable element, int index)
{
    VideoSelect videoSelect = null;

    if (element is Audio)
        //
    else if (element is Video)
        videoSelect = new VideoSelect(index, element.name, GetThumbnail(element.path, SystemData.thumbnailFrame));

    videoSelect.Location = GetElementsPosition(index);

    panel_List.BeginInvoke(new Action(() => 
    {
        panel_List.Controls.Add(videoSelect);
    }));
}

private Bitmap GetThumbnail(string path, int frame)
{
    VideoFileReader reader = new VideoFileReader();
    try
    {
        reader.Open(path);

        for (int i = 1; i < frame; i++)
            reader.ReadVideoFrame();

        return reader.ReadVideoFrame();
    }
    catch
    {
        return null;
    }
}					

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using (VideoFileReader reader = new VideoFileReader())
{
  // ...
}					

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public void DisplayPlaylist(Playlist playlist)
{
    for (int i = 0; i < SystemData.usedDisplayingThreads; i++)
    {
        Thread thread = new Thread(() => DisplayElements(playlist, i));
        thread.Start();
    }
}

private void DisplayElements(Playlist playlist, int startIndex)
{
    for (int i = startIndex; i < playlist.elements.Count; i += SystemData.usedDisplayingThreads)
        DisplayElement(playlist.elements[i], i);
}