您可以以编程方式执行FFmpeg以生成缩略图文件。然后打开图像文件以根据需要使用它。

这是一些示例代码：

public static Bitmap GetThumbnail(string video, string thumbnail)
{
    var cmd = "ffmpeg  -itsoffset -1  -i " + '"' + video + '"' + " -vcodec mjpeg -vframes 1 -an -f rawvideo -s 320x240 " + '"' + thumbnail + '"';

    var startInfo = new ProcessStartInfo
    {
        WindowStyle = ProcessWindowStyle.Hidden,
        FileName = "cmd.exe",
        Arguments = "/C " + cmd
    };

    var process = new Process
    {
        StartInfo = startInfo
    };

    process.Start();
    process.WaitForExit(5000);

    return LoadImage(thumbnail);
}

static Bitmap LoadImage(string path)
{
    var ms = new MemoryStream(File.ReadAllBytes(path));
    return (Bitmap)Image.FromStream(ms);
}