Hi Cameron,
Thanks for your answer. The attached image is a crop of a screenshot of a fullscreen preview.
Honestly, having to understand the ~2000 lines of code (including a non trivial OpenGL shader) of the LoopThroughWithOpenGLCompositing sample just to display a full resolution video is like

. IMHO that's exactly the kind of things the SDK should take care of, and such a basic task should be done in a couple of hours.
Moreover (after I have understood that it must be run as root), the LoopThroughWithOpenGLCompositing doesn't show a video, just an OpenGL scene rotating on a black background.
I better understand now why Media Express does not have a fullscreen preview option

... Even BlackMagic's devs do not want to go that way
Luckily I have found that recent versions of GStreamer have a qmlglsink element, allowing to perfectly display a video (including from a DeckLink card) in a QML app. This takes ~ 150 lines of easily understandable code (sample available here:
https://cgit.freedesktop.org/gstreamer/ ... k?h=master). I'd have prefer to avoid the GStreamer dependency but I have to move on.
I'm extremely disappointed by the SDK.