Severe black bars glitching with OpenGL
When resizing the video (using OpenGL/EGL) with the mouse, the video keeps moving around until the mouse is released. This seems to relate to the placement of the video within the window, i.e. glitches get worse when the window aspect ratio gets further from the video aspect ratio.
This is tested under KWin/Wayland. This cannot be reproduced under Wayland+SHM video output due to #18045, so it's unclear if the bug is in the OpenGL video output.