Kdenlive - The Chroma Key effect

The Chroma Key is an audiovisual technique which allows to replace the background color, usually green or blue, with an image.

In this example we'll apply the Chroma Key technique with Kdenlive. First of all add one image and a video to the "Project Bin". Then, drag them both to the timeline, putting the video above the image. Next, select the video clip, go to "Effects", click on "Alpha manipulation" and double click on "Chroma Key". Then, change the "Color key" to green (you can even use the color picker). For better results, you can to adjust the intensity of the effect with the "Variance" option. And that's all. Finally, click on the Render" button if you want to render the project.

If you want to practise, you can find background images on http://freeimages.com and green screen footage on http://videvo.net.