A few years back, when I had a mp4 file of a movie, I used to make a MKV attaching the official poster of that movie to the final file. After the process, whenever I browsed the folder where that and other movie files which also had posters, the MKV file rendered itself with the image instead of the generic random one that the file browser shows. As a linux user, even today I’ve been trying to figure out how to recover this option, but it seems it’s not son commonly known, anyone here can give some feedback on this subject? Thank you very much.