I appear to have a bug affecting rendering a video with a mask. The monitor displays as expected, but the output appears unmasked. (I don't seem to be able to display images: 'It was not possible to determine the dimensions of the image') The mask is a white diamond on transparent background created with gimp (which I have found causing other problems) composited over the clip with 'multiply'. Why might this be happening?
This is not the first problem I've experienced with masks.
kdenlive 12.20.1 ubuntu 20.04