private void button1_Click(object sender, EventArgs e)
{
string html = "<html><head>";
html += "<meta content='IE=Edge' http-equiv='X-UA-Compatible'/>";
html += "<iframe id='video' src= 'https://www.youtube.com/embed/{0}' width='600' height='300' frameborder='0' allowfullscreen></iframe>";
html += "</body></html>";
this.webBrowser1.DocumentText = string.Format(html, textBox1.Text.Split('=')[1]);
}