I recently discovered the annotation abilities of marginnote with mp4 video files. This set of features is very innovative, forward thinking, and potentially very powerful!
The only drawback I see is that the user has to upload an mp4 file. While mp4 upload can be useful as a feature, I believe it would be more powerful to be able to add hosted online videos from YouTube, Kahn academy, Coursera, edX, LinkedIn learning, etc. Many class courses and lectures are hosted online and there is no solution that exists to markup and annotate these video notes in the way marginnote has the potential to with time stamped annotations and links!
+1 feature request for annotating hosted videos in marginnote !