i was in the need to create a video that displays two video sources in one frame, aka split screen. i tinkered and pondered, trialed and errored, and in the end i was able to accomplish this through rather weird circumstances.
You can view the effect here in a video i cut for a friend:
while the video itself maybe nothing to rave about, it displays the effect around 2/3 in the video (it's ~1min, so you won t wait long anyways). As I said, I could achieve the effect, but I am rather unsure how I did it. I roughly followed these three steps, (though while I wrote down, what I did, I could'nt reproduce this, so there may be a flaw in there):
1. put three clips on top of each other, the upper and the middle clip will be the clips being displayed, the 3rd clip will form the background.
2. add a composite transition to the 2nd clip, so it will be between the 2nd and the 3rd clip, select the transition and choose with the lower left icon "resize=50%". repeat this with the 1st clip, so that there is a transition between the 1st and the 2nd clip. Do the resizing.
3. Change both (or one) transitions to AffineComposite. Maybe redo scaling and positioning, switch back to normal Composite. If you were lucky, you are done.
As I said before, sometimes this results in the split screen effect, sometimes it doesn't. It looks to me like this feature is enabled through a bug when switching from normal composite to Affine and then back to normal results in the "split screen" effect, but on the other hand I am clueless what kind of magic is at work.
For myself I saved one kdelive-file with the working split-screen effect inside, kept the transitions the 'special transition' and just changed the clips in there new videos . If you are interested in using the effect for yourself, i will upload a kdenlive-file for your downloading pleasure. If there is an easy way to achieve the split screen effect and i came to ignore this, feel encouraged to share your knowledge.
ps: there is a wish filled in the mantis bugtracker, which gently asks for an intuitive way of doing split-screen videos. at the time you are viewing this, this may have been implented into kdenlive, so you might want to check: