I have an original video that looks like this: https://drive.google.com/open?id=19V0_F ... gYdcxGQ_6D
After rendering selected clips with kdenlive I get this: https://drive.google.com/open?id=1wDR6Q ... VZ1ryWXIKk

The dimensions of the original clip are 720 x 576, codec H.264
The dimensions of the rendered video are 1080 x 1920 H.264 - however I tried many other combinations in the render dialog to no avail. Also, why does this change anyway.

Can someone please give me a hint?
Thanks
Ole

1080x1920 - that is 1080p rotated by 90 degrees. Your 576 pixels will fill only a third of the output screen in height.

If you want to fit the small original clip into your project size, you wll have to use a position and zoom effect to enlarge your source video.