A frequent issue that appears in live video applications is how to label the various video streams that are being shown to the user. Using a text overlay is one approach. With a text overlay, the label appears somewhere inside the video window, so it covers part of the video.
When implementing text overlays, it is important to synchronize drawing the video image and the text to avoid flickering. The correct synchronization method depends on the details of how images are rendered on the screen, including screen refresh rate and whether double buffering is used or not.