|Description||Compositing actions in Kdenlive can be frustrating because it uses an unusual transition and compositing system.|
For example if you have a "burn" transition between two clips on track 2 and 3 and then place a video in track 1 that you want to dissolve into the result of the burn transition between 2 and 3, you can not simply add a transition between 1 and 2 but have to turn the transition between 1 and 3 because the result of a transition can only be received from the lowest of the involved tracks. As soon as you try to do more complex compositing you will get problems.
And alpha operations are only supported by the appropriate transitions. The most other NLEs support it directly so that an image with alpha channel or a semi transparent made video for example is composited with the layers below without the need of a transition. You can also change the blend mode instead of the need to use e.g. a multiply transition.
This brings the advantage that you can do more complex compositions more easily and you can composite images with alpha channels with blend modes. In kdenlive you can not composite a png image with alpha over in screen mode simultaneously for example because you had to use an alpha operation transition for alpha compositing and also a screen transition.
I know that Kdenlive is not intended to be a compositing program and that is all very difficult stuff, but I want to expose my thoughts because I had some bigger projects in the past that showed that this is a big limitation in Kdenlive's workflow.