Yuli Asencion has flagged up dotSUB, an excellent video subtitling platform. It has a nice built-in editor which allows you to create subtitles for your videos (upload or link to open-source clips). Once you have saved a copy, you or others can translate these subtitles into other languages. Useful, therefore, both for teachers to prepare materials - a difficult segment that learners will have difficulty following unaided, perhaps - and as a learning activity, if the learners subtitle the videos themselves.
Via Yuly Asencion, Shona Whyte