To develop from within
Hypothesis (hypothes.is) is an annotating tool, comes as an extension for Chrome Web browser, which runs as an overlay on any webpage or pdf (opened inside Chrome) and allows you to highlight and annotate content with collaborative features.
Is it really possible to annotate a video? Annotate.tv offers a solution close to that. Annotate.tv provides an optimized note-taking flow from Youtube videos, especially with ease.