You are doing something wrong. What you need to do is launch kdenlive, then select Project → Add Clip or Folder and select the video. Then drag it into the time

You are doing something wrong. What you need to do is launch kdenlive, then select Project → Add Clip or Folder and select the video. Then drag it into the timeline (I just did some googling the first time). The UI is somewhat clumsy but I think it is pretty good that we have an open source video editor.