Youtube is a treasure trove of visual content, including a lot of technical talks. Its search/discovery capabilities are weak though (possibly because there are so many normal users using it that their preferences have overtaken the system). It seems to me that knowing some good channels can help one find a lot of interesting content.
My own recommendations (mostly programming/CS):
- awesome lists on Github are a good place to find community-curated talks.
- https://dev.tube/ (a search engine that filters on whitelisted channels)
- [Two Minute Papers](https://www.youtube.com/user/keeroyz/videos)