The intermediary solution for me between ffmpeg and kdenlive is LosslessCut (https://github.com/mifi/lossless-cut). Also free and open-source... of course it look less cool than a Terminal UI like the OP, but it's very practical when I don't want to reencode everything, or if I just need to change the format of container (MP4, MKV, etc.).

You are welcome! It is nice when you need to quickly crop or trim something and don’t want to launch a video editing app. The repo is owned by a friend, you can leave a star to make him happy :)