recommended method to use OGL with QGraphicsView causes errors

In the doc on this page it says "To render using OpenGL, simply call setViewport(new QOpenGLWidget)"

However, doing so only produces a repeating stream of these errors:
Failed to activate video surface
QOpenGLFunctions created with non-current context
QPainterVideoSurface: Vertex shader compile error

Steps to reproduce:

1. on mac, on a fresh install of Qt Creator 4.13.1 (5.15.1), open the example "Video Graphics Item"
2. at the top of VideoPlayer::VideoPlayer, add this code: 
3. graphicsView->setViewport(new QOpenGLWidget());
4.  run and open an HD (1920x1080) h.264 movie, and play it

result: no video, lots of errors in log