Miteiru is an open source Electron video player to learn Chinese, Cantonese, and Japanese. It can play all Youtube and HTML 5 supported format (.mkv, .mp4, .mov, and many more) videos, and lots of supports on other subtitle formats (.srt, .ass, .vtt, and many more)
this needs some kind of hard video.js knowledge, hard to debug, easy to be done, this is not a large scope