One example application that does drawing over the video stream is BurgerFace. Unfortunately there is no source code available, however, jfk gave some guidance on technology he used to implement the application.

His replies can be found on here.

To sum up: jfk used SDL libraries to implement BurgerFace application. For capturing images from the camera he used V4L2, however he suggests gstreamer might be more user friendly. One of the reasons why he used SDL instead of xoverlays is that overlays cause flickering when drawn upon a camera stream. I also noticed this problem when i was changing the size of the camera stream window.

I also analyzed the qtcartonizer code in more detail and figured out that the application only draws on top of a static taken by the camera and not onto a live video stream. Therefore, the application does not face the limitation issue of the overlay.

Has anyone any idea what is causing this flickering in overlays and how to fix it? Unfortunately I have not got the source code to show you.

Thanks for help.
Klen