This is really fantastic! I have been looking for a good app for this for a while. It seems like there are several solutions for it, all emerging around the same time, which is great news for language learners!
Request: please add an option to not continue playing the video after I click "save". It is aggravating when there are several words that need to be saved at once and I have to pause the video quickly to get all of them.
You could also make the UI much smoother by copying the way the FluentU player works: pause the video and show a translation as soon as the user mouses over any subtitles. Unpause the video when they mouse away from the subtitles.
It would also be really helpful to have some contextual information saved with each word. The surrounding phrase would be helpful, for instance. It would be really fantastic to be able to save the screenshot (in low resolution to save space), but I understand if copyright prevents that somehow.
I really, really wish there were a more open solution for this. Has anyone else used LWT (Learning with Texts)? You could specify the dictionary API/URLs to use. (There were also really primitive word splitting regex settings, but I didn't find them very useful.) I want to be able to get more information on complicated words, from either compounding (German) or extensive morphology (Turkish). I want to be able to look up Chinese, Japanese, Vietnamese or Thai words; these languages require extra processing to extract words because they don't separate words explicitly. When studying Japanese or Chinese, I want to be able to save characters for later study, not just words.
In general I really wish I could dig in and add functionality that I know I would love but I'm not confident that a large enough audience to warrant core app changes would need.