Google Docs doesn't allow you to embed videos directly like you can with Slides. DocuTube Viewer reads your document and finds links to YouTube videos.
DocuTube Viewer loads any linked YouTube video in the document in the sidebar. You can watch videos without leaving your document! It even includes videos linked in comments, which is great for student feedback.
Search caused several issues, specifically when a user tried to open the Addon without having edit access to the doc. DocuTube Search will be run as a separate project on GitHub and released as a separate Addon.
DocuTube is currently under review for the Google Apps Marketplace, so you can't install it from there yet. In the meantime, you can copy this repo into your own script editor and try it yourself.