从中提取拇指管C＃中嵌入的URL

Question

我已经在C＃中编写了一个函数，它正在提取管内嵌URL的大拇指，但仅针对像“https://youtu.be/8YDKDfkTbZU”这样的URL，我无法提取实际的拇指。如何从这种URL中提取图像。它适用于像“https://www.youtube.com/watch?v=F2lN25IayH8”这样的URL。

这是我目前的代码

if( ShareHolocPostDesc.Contains( "youtube.com" ) )
                        {
                            int endPoint = ShareHolocPostDesc.IndexOf( "<iframe" );

                            ShareHolocPostDesc = ShareHolocPostDesc.Substring( 0, endPoint - 1 );
                            ShareHolocPostDesc = ShareHolocPostDesc.Replace( "<br/><br", "" );
                            string[] arrShareHolicDesc = ShareHolocPostDesc.Replace( "<br/><br", "" ).Split( "?v=".ToCharArray() );
                            string YouTubeVideoID = arrShareHolicDesc[arrShareHolicDesc.Length - 1];
                            YouTubeVideoID = YouTubeVideoID.Replace( "<br/>", "" );
                            YouTubeVideoID = YouTubeVideoID.Replace( "<br/", "" );
                            ogImage = "http://img.youtube.com/vi/" + YouTubeVideoID.Trim() + "/0.jpg";
                            }

  ShareHolocPostDesc="https://youtu.be/8YDKDfkTbZU <br/><iframe width='100%' height='450' src='https://www.youtube.com/embed/8YDKDfkTbZU'></iframe>"

请帮忙。