Display (SDL or GL) - CESNET/UltraGrid GitHub Wiki
For SW display (SDL/OpenGL) users:
As the video is displayed as a texture, your maximal XVideo overlay/texture size should be greater than the size of the video.
You can check this using the command:
$ xvinfo | grep 'maximum XvImage size'
If the value is lesser then the desired video size, try updating your video drivers. Recent NVidia or ATI proprietary drivers should be OK.