I'm using the latest kdenlive package and associated mlt, frei0r from sunab's svn repo, on Kubuntu 12.10.

What I want to achieve with kdenlive is this: a sequence of short clips is playing inside a fake polaroid image. This whole animated polaroid should then coming flying in and rotating at the same time until it reaches the center of the canvas where it sits still, but the animated minature clips in the polaroid still play.

My first attempt was to create the static polaroid containing the playing clips as a separate kdenlive project, say PolProj.

Next, I create the main project and add PolProj as a clip. I'm dragging this clip into the timeline and add an affine transition to it, setting the keyframed position and rotation. When I preview this in kdenlive, everything looks as expected. When I'm rendering (to H.264) it is all messed up: there are only the playing minature clips visible but not the static polaroid around it. The affine translation does not get applied at all.

Okay, so I went back to PolProj and rendered it into an mp4 file using the H.264 codec. Project and output resolution is 1920x1080. Next, I drag the final mp4 clip into my main project (and remove the kdenlive project clip from my first attempt above). When I add an affine effect to the clip in my timeline and add the keyframed translation and rotation, everything seems to be okay.

However rendering gives a strange effect: the polaroid has been magnified by maybe 5 or 10% and now stretches past the project canvas. This happens only in the rendered output.

Even more strange, adding a second rendered H.264 kdenlive clip and adding an affine effect to it does not cause any visible effect on this second clip at all.

Another strange thing I'm observing is that the rotation actually causes distortion, as if the pixel size is not square. Locking at the clip meta data does not reveal any problems: 1920x1080, pixel ratio 1:1.

Forcing the ratio to 16:9 now causes just the proxy clip to change it's aspect ratio, but when deleting the proxy clip, the original clip retains its proper aspect ratio. So the force causes the proxy to look different in aspect ratio compared to the original clip.

I'm totally lost at the moment at how to achieve my original idea using kdenlive. Any help is greatly appreciated.

Well, I can't answer you about rendering, but maybe this two tutorials can help you, because they work with multiple videos together:

Compositing Multiple Videos Together:
http://www.youtube.com/watch?v=aEu27QCQUb8

kdenlive multi clip:
http://www.youtube.com/watch?v=cFIRHOG86a0

Oh well, now there seems to be several things broken in kdenlive and mlt, unfortunately. I've new started the main project from scratch.

1. I had to disable proxy generation in order to successfully apply the affine translation without the translation distoring the clip. I don't know why this is so, but it seems that there is again something broken in proxy handling. The clips I'm pulling into my main project are H.264 mp4 clips, same 1920x1080p/25 as the main project. Pixel aspect ratio is correctly 1:1. Somehow kdenlive still messes up proxy generation. Sigh.

2. See screenshot attached -- I've put an alpha mask on each clip in order to mask out everything except the (fake) polaroid for each clip. As can be clearly seen, kdenlive completely corrupts the mask: yes, this is only one alpha mask set, but after some time, strange things happen and after saving the project, exit kdenlive, loading the project, kdenlive step by step destroys my project.

3. When rendering even more corruption occurs: sometimes clips are rendered as complete memory dump garbage. Sometimes, clips completely disappear from the final rendered output, or even the preview gets corrupted, but not always.

So at the moment, kdenlive seems to be in a bad condition...

If there is interest by the developers, I can provide further screenshots.

Another strange thing I noticed: I can't expand the clip in the timeline beyond its length in order to repeat the final frame.

...btw, it's not the first time, I'm working with multiple clips and composing them in complex ways, clipping them, et cetera. It is just that I've seem to hit some weak spots in kdenlive now. The aspect ratio problem, the alphamask problem, stills problem, not to mention speedup effect corruptions, ...

So I overhauled the main project again, this time avoiding the alphamask effect like the plague. Instead I used the clip&crop&pan effect as the polaroids are of a rectangular shape, so this works. As it turned out, mlt now correctly renders the whole shebang in both the preview and the final render output. I could also simplify the stills what formerly also caused mlt to do all kind of weird things.