I'd probably suggest animated webp. They're super small so they're fast to load. Browser support is limited but since it'd be specific to a course... User will just have to live with it. I do currently create webp for every png/jpg upload but I'm actually not sure if I accept webp uploads. What do you think? Whould that help you? Please do reach out per email, I'm definitely interested in supporting sign languages. That'd definitely be prioritized since I think it's important.