var
 hr: HRESULT;
 ClientConnections: IWMClientConnections;
 lwClients: LongWord;
begin
 hr := ASFWriter.WriterNetworkSink.QueryInterface(IID_IWMClientConnections, ClientConnections);
 if SUCCEEDED(hr) then
 begin
   hr := ClientConnections.GetClientCount(lwClients);
   if not FAILED(hr) then
   begin
     result:=lwClients;
   end;
 end;
end;

 var
   ClientConnections : IWMClientConnections;
 begin
     ClientConnections := ASFWriter.WriterNetworkSink as IWMClientConnections;
     ClientConnections.GetClientCount(Result);
 end;