how to display text on video screen?

Create a text layer, setlayer above everything else, create a timer for your message loop, use getmessage instead of wait on your port, check the timer and hide or remove the text layer when time is up

As mentioned in your other thread (viewtopic.php?f=34&t=86086), you cannot customize the roVideoScreen. To do what you're wanting, you'll likely need to implement your own custom video player with roVideoPlayer instead.