Nothing
output$video_intro <- renderUI({
HTML('<iframe width="90%" height="250px" src="https://www.youtube.com/embed/XX_bmCrI_gc?rel=0" frameborder="0" allowfullscreen></iframe>')
})
Any scripts or data that you put into this service are public.
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.