I recently started using Kdenlive to edit video, and so far I am very happy with it. There is only one problem: I would like to be able to create a video in 4:3 aspect ratio, but it must show correctly on a wide-screen (16:9 aspect ratio) TV set. In other words, I want pillarboxes on the side to prevent the picture from being stretched horizontally. I know this must be possible, because commercial DVD videos that are marked 4:3 show correctly on a wide-screen TV.

Does anyone know how I can do this?