Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Two good ones that were recently uploaded to youtube:
Paul Halmos (teaching): https://www.youtube.com/watch?v=6KWaBikjnYw
Yitang Zhang (bounded gaps between primes): https://www.youtube.com/watch?v=XIIyKWxGhEA
