I created a clip with kdenlive consisting of a poem's text scrolling vertically over a background video. The text is in a PNG image with transparent background which I created in the GIMP.
However, it wasn't that easy to get it to work because I started out with a pan & zoom effect on the PNG ... it is the same width as the video, but much higher because it scrolls from top to bottom over the length of the video, so it needed scaling and centering. When I got that set up, I added the background video clip to the second video track and added a Composite transition to the PNG image.
What happened next is puzzling to me. The text was shifted to the left, partly cut off at the left edge, and the right half of the screen showed only the background video. Then I tried resizing and centering it in the transition editor, but it got way too big. It seems that the scaling factors were interpreted cumulatively.
OK, but when I leave the scaling factor at 100% in the transition editor, why doesn't Kdenlive just take over the pan & zoom settings and leave it alone, superimposing the results of whatever effect there is above the transition, instead of messing around with the position and alignment?
To get it to work, I had to remove the pan & zoom effect entirely and do everything in the transition editor. Seems kind of counter-intuitive to me, though.