Source: Bookmark It – Chrome Web Store
Bookmark It is an extension for Google Chrome that allows you to bookmark and comment on the bookmark in a YouTube video.
The bookmarks and comments are not shareable, so the extension is useful in the classroom when a teacher wants to use a YouTube video in the classroom. The bookmarks allow the teacher to easily jump to specific places in the video.
Signing up for a free account allows you to sync the bookmarks and notes across browsers.