I recently prototyped a Youtube annotation interface. It's based around the Hypothesis annotation service. Let's you annotate youtube transcripts (approx 95% coverage from what I can tell) inline w/ the video itself. Super early sketch in code. Controls to play the video and sync it to the transcript. Full transcript search for keywords, etc. It was a fun project. Code is at
https://github.com/dwhly-proj/droppdf, major kudos to Paul Genho, who did the lifting. This is part of the overall document conversion, hosting and annotation service at docdrop.org-- which we'll incorporate natively into Hypothes.is.
Feedback on what's most important next. Submit or upvote at https://github.com/dwhly-proj/droppdf/issues