rendering MP4 video including meta data in Kdenlive. This is very convenient, as you keep the meta data (such as title, author, copyright) in the best place: in your Kdenlive project. Unfortunately, the underlying ffmpeg handles only some, but not all (usable) of the iTunes-compatible meta data elements. Even worse, ffmpeg cannot add cover art. Time for another attempt: a Kdenlive post-rendering script...
ffmpeg gets us on really difficult terrain. It sort of feels like we're back in the early days of MP3 audio files. Not much hard documentation and everyone seems to say something else. Fortunately, a dive into ffmpeg's source code allowed me to surface with a simple list of meta data supported for MP4 containers.