How to set the selected index of dropdownlist in form load

Having problem in playing youtube video in asp.net C#.
finally i want to accomplish changes at run time,while changing dropdown text.
it only plays zero index item,now how can i resolve this..

thanks in advance

namespace Skyaircon {     public partial class ProjectVideo : System.Web.UI.Page     {         #region init settings         // player width         private int _W = 640;         // player height         private int _H = 505;         // autoplay disabled         bool auto = false;         #endregion         #r ...