The YouTube Java Manage Threads Sample Code demonstrates how to create a top-level comment for a video and a channel, retrieve the top-level comments for a video and a channel, and update an existing comment using thread methods.
Twitter announced the Periscope Producer API, which will give third-party apps the ability to authenticate Periscope accounts and let people push live video from just about anywhere. The idea is to make it easier to share video from just about any device and reduce pain points for end users.
If you wonder which of the 267 APIs on this site people view most often you might be surprised. It's not Google Maps, it's YouTube. Which has been true for quite some time. But the number of mashups using YouTube has been small, until recently when they've started to pick-up.