Amara.org website is the best way to create captions and subtitles. You don't download anything, you just enter the site, you write Youtube, Vimeo, html links and then you add subtitles while watching the video and sync.
Especially with the Youtube videos, it is wonderful and easy to use. Synchronizing is also easy.
I use this site in projects (Etwinning, Erasmus+), when we upload a video in Turkish, my students use this site and translate into English. Then our partners add their videos in English and we translate it into Turkish. I know that translation method is the oldest method in English but it is useful for students to learn new vocabulary and use them.
Also you can use it for projects at school. Students can choose a video and translate it.